Effect of solution treatment and aging on microstructure and tensile properties of high strength β...

Accepted Manuscript

Technical report

Effect of Solution Treatment and Aging on Microstructure and Tensile Proper-

ties of High Strength β Titanium Alloy, Ti-5Al-5V-5Mo-3Cr

Shashi shekhar, Rajdeep Sarkar, Sujoy Kumar Kar, Amit Bhattacharjee

PII: S0261-3069(14)00283-0

DOI: http://dx.doi.org/10.1016/j.matdes.2014.04.015

Reference: JMAD 6406

To appear in: Materials and Design

Please cite this article as: shekhar, S., Sarkar, R., Kar, S.K., Bhattacharjee, A., Effect of Solution Treatment and

Aging on Microstructure and Tensile Properties of High Strength β Titanium Alloy, Ti-5Al-5V-5Mo-3Cr, Materials

and Design (2014), doi: http://dx.doi.org/10.1016/j.matdes.2014.04.015

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers

we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and

review of the resulting proof before it is published in its final form. Please note that during the production process

errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

http://dx.doi.org/10.1016/j.matdes.2014.04.015

http://dx.doi.org/http://dx.doi.org/10.1016/j.matdes.2014.04.015

1

Effect of Solution Treatment and Aging on Microstructure and Tensile -5Al-5V-5Mo-3Cr

Shashi shekhara, Rajdeep Sarkara, Sujoy Kumar Karb, Amit Bhattacharjeea

a Defence Metallurgical Research Laboratory, Hyderabad-500058 b Indian Institute of Technology, Kharagpur-721302 Corresponding author. Tel.: +91 40 2458 6455, +91 8008836342; fax: +91 4024342123 E-mail Address: [email protected], [email protected] , [email protected] Abstract Ti-5Al-5V-5Mo-

size components in aircraft structures replacing Ti-10V-2Fe-3Al. In the present study, a

double VAR melted ingot was thermo-mechanically processed and it's microstructure and

aging resulted in an optimum combination of strength and ductility. Its aging behavior was

studied as a function of time and temperature and corresponding microstructure as well as

fractographs of tensile tested specimens were recorded. This systematic study should help in

further modeling its mechanical behaviour.

Keywords: Titanium alloy, Processing, Solution treatment, Aging, Microstructure, Tensile behaviour, Fractography.

2

1.0 Introduction

-6Al-

metastable and stable alloys and inter-metallics (Ti3Al and TiAl based alloys).

titanium

retention of bcc ( ) phase on rapid cooling to room temperature. Strengthening by

Despite their advantages, alloys have also their limitations. The reasons for the

limited use of these alloys include relatively higher costs, more complex processing routes,

from these other disadvantages include their microstructural instabilities, mechanical

properties that are sensitive to minor process variations,potential problems during melting,

low ductility in high strength weldments, not enough experience and a lack of sufficient

interest.

Ti-5553 (Ti-5Al-5V-5Mo-

modification of the Russian alloy VT-22 (Ti-5.7Al-5.1V-4.8Mo-1Cr-1Fe). The applications

of Ti-5553 alloy in aerospace industry are typically in high strength airframe components like

landing gears and flap tracks. It has replaced Ti-1023 (Ti-10V-2Fe-3Al) alloy in almost all

the aerospace applications as it has higher hardenability and is therefore preferred for thick

section forgings. In the recent Boeing aircraft models, these alloys are preferred over Ti-64

(Ti-6Al-4V) due to their high yield stress, better ductility and higher fracture toughness. Also

the low modulus, low forging temperature and high oxidation resistance of these alloys make

it suitable for fabrication of even smaller aircraft parts [1]. There is a significant difference in

processing difference between Ti-5553 and Ti-1023. It is possible to air cool Ti-5553

following solution treatments without property deterioration [2]. In comparison, Ti-1023

components have to be water quenched to achieve the same result, limiting their section

thickness to 76 mm, as compared to the 152 mm possible with T-5553 [2]. In addition,

Fanning et al. [3] have also reported that the thermo-mechanical process-ability of Ti-5553 is

more robust. They further have stated that the new suppliers who have got involved with Ti-

1023 forgings have almost always had to go through a learning curve to achieve the required

3

strength, ductility and toughness. On the other hand several suppliers have provided Ti-5553

forgings meeting these requirements with their initial attempts.

The mechanical property of an alloy depends on its thermo-mechanical processing

and heat treatment. Ti-5553, just like other alloys is thermo-mechanically deformed in the

solution treated in either phase field to vary the amount and morphology of

primary phase and then aged at lower temperatures in the phase field to obtain

precipitates of fine secondary

the distribution of different shape, scale and

such as Mo and Cr in Ti-5553, the

that of Ti-1023. Ti-5553 alloy on solution treatment, quenching and aging produces a

microstructure consisting of different morphologies of phase in matrix. It is possible to

obtain both equiaxed and/or elongated distribution of phase in the microstructures

depending on whether the deformation and solution treatment has been carried out below or

There have been several studies on similar type of alloys. The effect of processing and

heat treatment has been studied on tensile properties and fracture toughness of a high strength

metastable beta titanium alloy, Ti 10V 2F3e 3Al by G. Srinivasu et al. [4]. Microstructure

and mechanical properties of a new high strength Ti 3.5Al 5Mo 6V 3Cr 2Sn 0.5Fe alloy

were investigated in both the and solution treatment and subsequent aging at

temperatures ranging from 440 °C to 560 °C for 8h to investigate the relationship between

microstructures and properties by Zhaoxin Du et al. [5]. The influence of aging temperature

and time on the microstructure and properties of Ti-60, a high temperature titanium alloy has

been investigated by Weiju Jia et al. [6].A systematic variation of processing parameters has

been carried out on Ti 5Al 5V 5Mo 3Cr alloy to generate different beta annealed

microstructures, in terms of their dimensions in this alloy and quantitative measurements of

microstructural features have been carried out using stereological procedures by Atasi Ghosh

et al. [7]. In another study by Sujoy kar et al. [8], a quantitative microstructural

characterization, using stereological methods, on various microstructures developed through

4

variations in separate heat treatment variables, as well as variation in each of the different

individual variables of a set of sequential combined thermo-mechanical processing steps to

obtain beta annealed microstructure of Ti-5553. Sujoy Kar et al. [9] have also developed a

predictive tensile property model for -processed Ti-6Al-4V alloy

Although there have been quite a few studies on same or similar type of alloys as

brought out above but still the microstructure-property relationship of this alloy is not studied

exhaustively.One of the earliest systematic heat-treatments studies on this alloy was done by

Orlova et al. [10]. Two heat treatment schedules were mainly followed. Schedule 1 was

solutionizing, stabilization and air cooling to room temperature followed by aging. Schedule

2 on the other hand consisted of direct furnace cooling the sample to the aging temperature

after the solutionizing and stabilizing treatments. A range of temperatures were chosen for

these heat treatments and etching techniques were used to distinguish between different

microstructures. It was found that solutionizing temperature determines the grain size and the

Fanning et al. [11] had provided quite considerable mechanical property data about

the alloy but without much microstructural details and correlation. NG Jones et al. [12]

carried out a comprehensive study of the thermo-

behaviour and also presented different resulting microstructures. Another study by NG Jones

et al. [13] focussed on as a precursor to phase precipitation and explained how chevron

shaped formation takes place on aging.

This study presents the result of a systematic preliminary study done on the

development of Ti-5553. The alloy was double vacuum arc re-melted and then thermo-

mechanically processed into plates. Tensile properties of the alloy were then studied as

function of different solution treatment temperature and aging time and temperature. Typical

microstructures of this alloy in different heat treatment conditions have been presented and

have been used to explain the tensile properties obtained. Only limited amount of data on this

alloy is available and the prime aim was to establish structure property correlation in the alloy

starting from thermo-mechanical processing. The authors feel that this kind of comprehensive

study on this alloy has not been presented.

5

2.0 Experimental Procedure

2.1 Melting

The alloy was double melted by vacuum arc re-melting (VAR) in a 40 Kg vacuum

furnace. The melting was done in a water cooled copper crucible. The bottom of the

secondary ingot was cut and discarded and the surface was also machined to remove the

contaminated layer and the irregularities.Defective portions at the top, containing pipe were

also removed. The turning from the top and bottom of the ingots after removing the defective

portions were sent for chemical analysis and the analysed chemical composition of the alloy

is given in Table-1 and 2. A combination of analytical techniques including JY-ULTIMA

make inductively coupled plasma optical emission spectrometer (IPC-OES) for elemental

analysis, LECO TC-600 for Oxygen and Nitrogen analyser and LECO RH-404 for hydrogen

analyser were used to obtain the chemical composition.

In ICP-OES system, in order to carry out analysis, the sample in form of turnings ( ~0.1 g

in a typical experiment) was dissolved in a microwave accelerated reaction system (MARS)

using 12 mL of Aquaregia +1 mL of HFand then diluted to 1000 mL by adding distilled water.

This solution was then aspirated into the plasma in order to perform the ICPOES analysis of the

light emitted from the elements present in the sample in the analysis. The LECOTC-600

instrument works on the principle of inert gas fusion technique coupled with IR and thermal

conductivity analyzers. A sample in the analysis is taken in a graphite crucible and fused by

resistive heating O is converted to CO/CO2 and is detected and quantified by an IR (infra-red)

cell, whereas the N2 content is detected by a thermal conductivity cell. For H analysis, similarly

in LECO RH-404 sample is heated in a graphite crucible, the hydrogen content present in the

sample evolves, which is carried to the thermal conductivity (TC) cell by the help of Argon

carrier gas and analysed.

formula [14] and then five samples were taken each from top and bottom of the ingot in as

cast condition and were solution treated at various temperature both above and below the

estimated beta transus temperature and examined metallographically. The specimens were

heated to 820, 830, 840, 850 and 860 C and soaked for 1hour (h) in an electric heat treatment

furnace and were then water quenched. The 850°C and 860°C treated specimens are

6

completely in the phase regime, hence the temperature of the alloy is 850+5°C

.

2.2 Thermo-Mechanical Processing

After machining of the surface and removal of the pipe portion from the ingot (143

region at 1050°C/2h and then forged to 65 mm thick plate.

Subsequently the 65mm plate was soaked at 800

mm thick plate. The 30 mm thick plate was further rolled down to 15 mm thick plate in a hot

rolling mill after soaking at 800°C for 1h. Water suspended glass solution Deltaglaze FB

412® coating of Henkel was applied on the ingots/ billets and plates prior to any thermo-

mechanical processing in order to reduce oxidation of the alloy during forging and rolling and

also to reduce the friction between the die/roll and the work-piece. The heavy reduction in the

region has resulted in breaking down of the grain boundary as well as the present

within the grains as shown in Fig. 1.

2.3 Heat Treatment

Since the alloy is relatively new, sufficient literature/information on the mechanical

properties of the alloy is scarce. In order to study and understand tensile behaviour of this

alloy under different microstructural conditions, investigation have been c

order to explain the different heat treatment cycles imparted in this study, a pseudo binary

phase diagram and a schematic for different heat treatment cycles are shown in Fig. 2a and 2b

respectively.

2.4 Sample Preparation

After heat treatment Ti-5553 samples were mounted with phenocure (Buehlar make)

mounting material in a Buehler SimplimetTM automatic mounting press. These mounts were

polished in the Allied High Tech MultiprepTM automatic sample preparation system with 400,

600, 800, 1000 & 1200 grit SiC paper. Finally they were placed for 12 h in the Buehler make

Vibromet polisher VibrometR in 0.05 µm non crystallising Colloidal Silica suspension for

final polishing. After polishing, samples were rinsed with distilled water and acetone.

Samples for light microscopy were etched by using etchant of 2% HF and 6% HNO3 in

distilled water. Samples for scanning electron microscopy were cleaned in acetone in

7

ultrasonic cleaner. Backscattered electron (BSE) images were obtained by using a FEI

Quanta 400 environmental scanning electron microscope (ESEM) operated at 20 kV and a

spot size of 3.5. For the examination of fracture surface of tensile tested specimens, the

secondary electron imaging mode of the SEM was used at 20 kV and a spot size of 3.

Specimens for transmission electron microscopy (TEM) characterization were prepared by

mechanically polishing the alloy discs of 3 mm dia. down to 100 m on different grits of

emery paper from 400 to 800 and subsequently electro-polishing these foils in twin jet electro

polisher (FISCHIONE Instruments, Model 110). Electro-polishing was done using 5%

H2SO4 solution in methanol as electrolyte at -50°C. During polishing, the voltage was

maintained at 20 V. The foils were examined using a Tecnai G2 20T transmission electron

microscope at 200 kV.

2.5 Property Evaluation

For tensile property evaluation, ASTM: E8 sub-size sample (gauge length=20 mm,)

were prepared and then tested on 100 kN Instron 5500 testing system at a constant crosshead

speed of 1mm/min (strain rate ~ 10-4) at room temperature. Test was conducted on two

samples for each condition and average value with its standard deviation has been reported.

Tensile properties like 0.2% yield strength (YS), ultimate tensile strength (UTS) and ductility

were determined as a function of ageing time and temperature.

3.0 Results and Discussion

3.1 Microstructure

C/1h/WQ) is

estimated to be 160 ± 3.9 µm. The TEM micrograph of Ti-

aged condition at 450°C for one and eight hours are shown in Fig. 4a and b; a fine acicular

precipitation is observed which coarsens with time during aging. The Selected Area

Diffraction (SAD) pattern [110] zone axis of phase after one hour of aging shows streaking

(Fig. 5a) but existence of diffracted spot from is not very clear due to the presence of extra

8

spots which are due to multi- phase [15]. But once the specimen

was tilted around (112), the presence of SAD spots from could be distinctly visualized at

the 1/3rd and 2/3rd position along (112) diffracted spot and transmitted beam as shown in Fig.

5b. With increase in aging time, there is negligible presence of and precipitation and

growth of precipitates takes place. NG Jones et al. [16] has also reported that further aging

only resolvable at TEM level and coarsen with time during aging (Fig. 4c-d). On aging at

600°C for four hours, fine are resolvable at SEM level (Fig. 6a), which grew

precipitates appear t

grain boundaries and secondly, from a large number of homogenously distributed intra-

granular nucleation sites (Also reported by S. Nag et al. [17]). These precipitates also seem

to possess two different morphologies, an acicular morphology and a fine non-descriptive

morphology. This phenomenon is more pronounced for higher aging temperatures and time.

The microstructures of the alloy which was solution treated (ST) in the phase

field at two different temperatures, 825°C and 800°C for 4h are shown in Fig. 7a and b

treatment. Stereological methods described in Searles et al. [18] has been used to characterize

microstructural features. The volume fraction of primary alpha after ST at 825°C/4h/WQ

0.84 µ µm. The globular primary at the grain boundaries

restricts the growth of the grains, thereby increasing ductility. Moreover it may be observed

that the phase has still not re-crystallised and it almost forms a continuous matrix of

phase interspersed with globular phase in the microstructure (Fig. 7a-b).

In the specimens aged at 450°C for up-to 16h, the secondary precipitation is so fine

for both the STA conditions. On aging at 550°C, very fine precipitatio

is visible for both solution treatment and aged conditions. On aging at higher

9

temperatures (600°C and 650°C) and time, re-crystallisation is observed as is clearly visible

in Fig. 8a and b for both the solution treatment conditions respectively. At higher

temperatures of aging, the secondary coarsening has been found to be slightly more in

comparison to aging at lower temperatures. Thicker grain boundary forms for higher time

and temperature of aging. The grain size in solution treated and aged microstructures

are much finer in comparison to

-5 µ

p)

ST temperature and the precipitation kinetics of further phase formation during aging

becomes sluggish for lower ST condition and results in finer and lesser secondary

precipitation. The secondary precipitation in this alloy occurs both along the grain

boundaries as well as within the grains at higher aging temperatures.

3.2 Tensile Properties

condition which results in enhancement in strength and reduction in ductility due to

precipitation of secondary

depends upon aging temperature and time. Tensile properties, thus, are strongly influenced by

aging time and temperature. The effect of aging time and temperature is shown in Fig. 9a and

b.

strength levels are attained but most of them break in the elastic regime. The reason for such

high strength and low ductility at low aging temperature/timealthough not very clear but

might be due to the presence of both fine and precipitates (only resolvable at TEM level)

along with coarser grain size. There is negligible presence of and the size of the

precipitates increases with increase in aging time and temperature and the ductility improves.

10

On aging at 600°C, strength is still quite high (1100-1452MPa) for all aging times and there

is slight increase in ductility at higher aging times (Fig. 9b) in comparison to that at lower

Similar trend is followed on aging at 650°C. Lower yield strength and higher ductility at

it determines the

also restricts the grain size by pinning the grain boundaries.

The tensile properties of the alloy in ST1 (825°C/4h/WQ) but aged at different

with an enhanced ductility of 16 ± 3.8%. Tensile properties of a

(800°C/4h/WQ) and aged at different temperatures and time is shown in Fig. 11. 0.2% yield

T1, the strength and ductility vary with aging temperature (Fig. 10a & b).

The maximum strength is obtained on aging at 450°C. For aging at 450°C, the strength

progressively with time during aging. This enhanced the strength. On aging at 550°C, the

equilibrium precipitation is reached faster (4h) and we do not see much variation in strength

after that. Some coarsening took place with increase in aging time; hence there is slight drop

in strength. At an aging temperature of 600°C, a slowly increasing trend in strength is

observed with increase in time of aging. On aging at 650°C, the maximum strength is reached

in the early stages of aging (4h) and then the precipitated secondary phase starts coarsening

leading to a drop in 0.2% yield strength on aging for longer times. Maximum ductility was

obtained on aging at 650°C for 16h of aging time (Fig. 10b).

is

h and lower ductility

11

aging time. At an aging temperature of 600°C, strength decreases considerably with increase

at 650°C, maximum strength was attained in the early stages of aging then precipitated

ng leading to a drop in 0.2% yield strength on aging for

longer times.

3.3 Fractography

A few samples were selected for fractography study in both solution treated and

solution treated and aged condition in order to identify underlying deformation/fracture

mechanism that control the tensile properties.

12-

fractograph of Fig. 12a and shallow and fine dimples are seen clearly in the high

solution treatment of the alloy leads to a mixed mode but predominantly faceted inter-

granular type of fracture (Fig. 13a, b & 14a, b). The true fracture strain for the above

conditions are zero (Table 3a) which points to a localized deformation. On increasing the

aging temperature to 600°C and 650°C, the fracture still appears to be of mixed mode type

but with more dimpled regions surrounding the facets and the area fraction of faceted regions

is lower as may be observed in Fig. 15a, b & 16a, b. Dimples though are still shallow in most

of the cases. The dimple size is very non uniform with sizes ranging from 0.1 µm to 2 µm.

different sizes as is evident from the relevant fractographs. Even after four hours of aging at

650°C, the true fracture strain still remains low.

(800°C/4h/WQ) shows a completely ductile mode of tensile failure (Fig. 17a & 22a). The

high magnification fractographs of Fig. 17b and 22b show fine and deep dimples. For both

type of failure (Fig. 18a, b& 19a, b) and (Fig. 23a, b and 24a, b) interspersed with brittle

12

facets. On aging at 600°C, the dimpled regions appear to have increased (Fig. 20a, b & 25a,

aging the specimen at 650°C after solution treatment, the fracture is completely ductile

with fine and deep dimples as shown in (Fig. 21a, b & 26a, b) with almost no facets.

shape and size are not very regular. There is no direct correlation between the dimple sizes in

both STA conditions but it appears that dimple size (~4 µ p is smaller than that

p (~6µ

and aged condition is hig

these observations point to the fact that aging after a lower solution treatment temperature

leads to a finer precipitation of secondary on aging that enhances the strength and reduces

the ductility. This is also borne out by the fact that the dimple sizes are slightly smaller in

case of lower temperature of solution treatment and aging. Since in titanium alloys, the voids

are known to initiate at the interfaces of and , therefore a finer secondary in case of

lower solution treatment temperature of 800°C leads to a finer void size.

Comparison of tensile properties in all three solution treatments and aged conditions:

Both strength and ductility increase with decreasing solution treatment temperature. The

strength in ST conditions in comparison to ST condition is higher since the

microstructure in the latter condition consists of two phases and the grain size is also finer.

For solution treated and aged conditions, following conclusions may be drawn:-

C/4h/WQ) condition has higher

(800

-29).

C/1h/WQ) condition, intermediate for

C/4h/WQ) for a given aging

temperature and time (Fig. 27-29).

13

P

volume fraction from 9 to 16 % reduces the ductility.

[5]).

result in optimum combination of strength and

4.0 Conclusions

In present study, microstructures in different solution treatment and aged conditions of

Ti-5553 have been studied. Tensile properties were

determined and fractography was carried out and analyzed for all the heat treatment

conditions. The result can be summarized as:

treatment.

(2). The secondary precipitation in both solution treated and aged conditions are not

resolvable at lower aging temperatures at SEM level although they are visible for

higher aging temperatures. They become coarser with increase in aging time and

temperature and possess both acicular as well as a non-descript morphology.

and lower d

(4). The and aging leads to higher tensile strength and lower ductility in

comparison to

show a

a dimpled fracture surface.

Acknowledgement

14

We are thankful to all members of titanium alloy group of Defence Metallurgical

Research Laboratory (DMRL) for carrying out the melting of the alloy and the members of

the metal working group of DMRL for carrying out forging and rolling of alloy. Lastly, we

express our deep sense of gratitude to Director, DMRL Dr. Amol A. Gokhale for his support

References

[1]. Luetjering G, Williams JC. Titanium, Engineering Materials and Processes.Springer Publication, 2nd Edition;2007. [2]. Jones NG, Dashwood RJ, DyeD and Jackson M. The flow behavior and microstructural evolution of Ti-5Al-5Mo-5V-3Cr during subtransus isothermal forging. Metallurgical and Material Transaction A 2009;40A:1944-54. [3]. Fanning JC, Boyer RR. Properties of TIMETAL 5553-A new near beta titanium alloy for airframe components. Ti-- Science and Technology 2003;IV:2643-50. [4]. Srinivasu G, Natraj Y, Bhattacharjee A, Nandy TK, Rao Nageswara GVS. Tensile and fra -10V-2Fe-3Al, as a function of rolling and solution treatment temperature. Materials and Design 2013;47:323-30. [5]. Du Zhaoxin, Xiao Shulong, Xu Lijuan, Tian Jing, Kong Fantao, Chen Yuyong. Effect of heat treatment on microstructure and mechanical properties of a new high strength titanium alloy. Materials and Design 2014;55:183-90. [6]. Jia Weiju, Zeng Weidong, Yu Hanqing. Effect of aging on the tensile properties and microstructures of near alpha titanium alloy. Materials and Design 2014;58:108-15. [7]. Ghosh Atasi, Sivaprasad S, Bhattacharjee A, Kar SK. Microstructure-fracture toughness correlation in an aircraft structural component alloy Ti-5Al-5V-5Mo-3Cr. Materials Science and Engineering A 2013;568:61-7. [8]. Kar Sujoy, Ghosh A, Fulzele Nishant, Bhattacharjee A. quantitative microstructural characterization of a near beta Ti alloy, Ti-5553 under different processing conditions. Materials Characterisation 2013;81:37-48. [9]. Kar S, Searles T, Lee E, Viswanathan GB, Tiley J, Banerjee R, Fraser HL. Modeling

Transactions A 2006;37A:559-66. [10]. Orlova LM. Metallographic Study of Solid Solution Decomposition for Titanium Alloy VT22.Metal Science and Heat Treatment (Russia) 1986;28(1):73-7.

15

[11]. Fanning JC. Propeties of Timetal 555 (Ti-5Al-5Mo-5V-3Cr-0.6Fe). Journal of Materials Engineering and Performance 2005;14(6):788-91. [12]. Jones NG, Dashwood RJ, Dye D, Jackson M. Theromechanical processing of Ti-5Al-5Mo-5V-3Cr. Material Science and Engineering A 2008;490:369-77. [13]. Jones NG, Dashwood RJ, Jackson M, Dye D. Development of chevron-precipitates in Ti-5Al-5Mo-5V-3Cr. ScriptaMaterialia 2009;60(7):571-73.

alloys. Metallurgical and Material Transaction A 1979;10A:132-34.

[15]. Sarkar R, Ghosal P, Muraleedharan K, Nandy TK, Ray KK. Effect of Boron and carbon addition on microstructure and mechanical properties of Ti-15-3 alloy. Materials Science and Engineering A 2011;528:4819-29.

-5Al-5Mo-5V-3Cr. ActaMaterialia 2009;57:3830-39. [17]. Nag S, Banerjee R, Srinivasan R, Hwang JY, Harper M, Fraser HL. Omega assisted nucleation and growth of alpha precipitate in Ti-5Al-5Mo-5V-3Cr-ActaMaterialia 2009;57:2136-47. [18]. Searles T. Rapid Characterization of Titanium Microstructural Features for Specific Modeling of Mechanical Properties. J. Measurement Sci. Technology 2005;16:60-9. [19]. Duerig TW, Williams JC. Overview-

-AIME 1984:19-64. [20]. Williams JC. Kinetics and Phase Transformations: A Critical Review. Titanium Science and Technology 1973:1433-94. [21]. Bhattacharjee Ametastable Laboratory, India;2006.

16

List of Tables

Table1: Elemental wet chemical analysis of the ingot. Table2: Gas analysis of the ingot. Table3: (a) Variation of C/1h/WQ) condition for constant aging time of 4h as a function of aging temperature, (b) Variation of true

C/4h/WQ) condition for constant aging time of 4h as a function of aging temperatur(800 C/4h/WQ) condition for constant aging time of 4h as a function of aging temperature.

17

List of Figures

Figure 1: Microstructure of the rolled plate. The plate was soaked at 800°C for 1 hour and

rolled down to 15 mm thickness from 30 mm initial thickness. The heavy reduction has

grains.

Figure 2: (a) Pseudo binary phase diagram of alloy showing all three solution treatment and

aging treatment. (b) A schematic of the different heat treatments carried out in the present

study on a time temperature plot.

Figure 3: Optical microstructur

Figure 4

specimen at (a) 450°C/1h/AC and (b) 450°C/8h/AC (c) 550°C/1h/AC and (d) 550°C/8h/AC,

temperature and time.

Figure 5: -phase showing a number of diffracted

could be distinctly seen at the 1/3rd and 2/3rd positions along (112) diffracted spot and

transmitted beam as shown.

Figure 6

se within

18

Figure 7: Electron back scatter micrographs of the alloy which has been imparted sufficient

4h/WQ (containing 9 volume

Figure 8: SEM micrographs of specimens + solution treated (a) 825°C/4h/AC and aged at

650°C/4h/AC and (b) 800°C/4h/AC and aged at 650°C/4h/AC, showing the presence of fine

globular primary present at the grain boundaries as well as within the grains and

tributed throughout. Fine re-crystallised grains are

Figure 9

aging temperature and time (a) 0.2% yield strength vs. aging time showing decrease in

strength with increase in aging time at a particular aging temperature and (b) % elongation vs.

aging time showing negligible elongation in case 450°C & 550°C and increase in elongation

at 600°C and 650°C for a given aging time.

Figure 10



aging time showing increase in ductility with increase in aging time at a particular

temperature.

Figure 11

of aging temperature and time (a) 0.2% yield strength vs. aging time showing constant

strength with increase in aging time for 450°C and 550°C and decrease in strength at higher

aging temperature and (b) % elongation vs. aging time showing increase in ductility with

increase in aging time at a particular temperature.

Figure 12: Fractographs of room temperature tensile tested specimen of Ti-

(885°C/1h/AC) condition showing (a) overall fracture surface, which appears ductile with a

few faceted features (b) magnified image showing shallow dimples.


(885°C/1h/WQ) and aged (450°C/4h/AC) condition (a) low magnification image shows

19

primarily brittle/crystalline fracture features and (b) high magnification micrograph shows

faceted and intergranular feature on the facets. In some region secondary cracks are also seen

(shown by arrows).




faceted and intergranular feature on the facets.




faceted and intergranular features surrounded by shallow dimples.


(885°C/1h/WQ) and aged (650°C/4h/AC) condition (a) low magnification fractograph shows

mixed mode type of fracture and (b) high magnification fractograph showing faceted features

surrounded by fine and shallow dimples indicating a mixed mode fracture.

Figure 17: Fractographs of room temperature tensile tested specimen of Ti-5553 in (825°C/4h/WQ) condition, showing (a) overall fracture area, which appears ductile and (b)

magnified image showing fine and deep dimples.

Figure 18: Fractograph of room temperature tensile tested specimens of Ti-5553 in

(825°C/4h/WQ) and aged (450°C/4h/AC) condition (a) low magnification fractograph

showing ductile failure mode and (b) high magnification fractograph showing fine dimples.

Some secondary cracks are also seen.

Figure 19: Fractograph of room temperature tensile tested specimens of Ti-

(825°C/4h/WQ) and aged (550°C/4h/AC) condition. SEM micrograph at (a) low

magnification and (b) higher magnification shows mixed mode of intergranular and ductile

fracture features. Ductile failure features are more prominent.

Figure 20: Fractograph of room temperature tensile tested specimens of Ti-5553 i

(825°C/4h/WQ) and aged (600°C/4h/AC) condition showing ductile fracture features at (a)

low magnification and (b) high magnification.

20


(825°C/4h/WQ) and aged (650°C/4h/AC) condition showing completely ductile failure mode

at (a) low magnification and (b) high magnification.


(800°C/4h/WQ) condition showing (a) overall fracture area, which appears ductile and (b)

magnified image showing deep dimples.

Figure 23: Fractograph of room temperature tensile tested specimens of Ti- ST2

(800°C/4h/WQ) and aged (450°C/4h/AC) condition(a) low magnification showing ductile

failure mode and (b) high magnification showing fine dimples. Some secondary cracks are

also seen.

Figure 24: Fractograph of room temperature tensile tested specimens of Ti -

(800°C/4h/AC) and aged (550°C/4h/AC) condition showing predominantly ductile failure at

(a) low magnification and (b) high magnification. SEM micrograph shows mixed mode of

inter-granular and ductile fracture features at higher magnification. Ductile mode is more

prominent.


(800°C/4h/WQ) and aged (600°C/4h/AC) condition, showing completely ductile dimpled

failure at (a) low magnification and (b) high magnification.


ST2(800°C/4h/AC) and aged (650°C/4h/AC) condition, showing completely ductile dimpled


Figure

temperature at a fixed aging time of 1h (a) 0.2% yield strength vs. aging condition

(X°C/1h/AC) showing decreasing strength with increase in aging temperature for given time

and 550°C, sample broken in elastic range) and (b) % elongation vs. aging condition

(X°C/1h/AC) showing increase in ductility with increase in aging temperature for given 1h of

aging time.

Figure


21


and 550°C, sample broken in elastic range) and (b) % elongation vs. aging condition


aging time.

Figure



and 550°C the sample broke in the elastic range) and (b) % elongation vs. aging condition

(X°C/16h/AC) showing increase in ductility with increase in aging temperature for given 16h

of aging time.

Figure 30: Plot of % elongation Vs 0.2% yield strength of Ti-5553 in all solution treatment

and aging condition investigated in this study. The encircled region represents optimum

combination of strength and ductility.

22

TABLE 1:Elemental wet chemical analysis of the ingot

Sample

(Ti5553)

Al (%wt.) V (%wt.) Mo (%wt.) Cr (%wt.) Fe (%wt.)

Top

Bottom

5.80

(±0.10)

4.80

(±0.06)

5.06

(±0.05)

2.70

(±0.09)

0.1

(+0.01)

5.80

(±0.08)

4.80

(±0.09)

5.00

(±0.07)

2.24

(±0.04)

0.09

(+0.01)

TABLE 2: Gas analysis of the ingot

Sample

Hydrogen(ppm) Oxygen(ppm) Nitrogen(ppm)

Ti-5553 30

(±5)

920

(±100)

< 20

TABLE 3 (a) 885 C/1h/WQ) condition for a

constant aging time of 4h as a function of aging temperature.

Aging condition

Volume p

UTS

(MPa)

True Fracture

strain

%RA

450 C 0 1187 0 0

550 C 0 1341 0 0

600 C 0 1314 0.01 0.75

650 C 0 1147 0.02 2.0

23

TABLE 3 (b): Variation of true fracture strain in 1 (825 C/4h/WQ) condition for a constant

aging time of 4h as a function of aging temperature.

Aging condition

Volume p

0.2% YS

(MPa)

True Fracture

strain

%RA

450 C 9.3% 1379 0.05 4.5

550 C 9.3% 1166 0.13 11.9

600 C 9.3% 1028 0.21 19.1

650 C 9.3% 1076 0.25 22.3

TABLE 3 (c): Variation of true fracture strain in 2 (800 C/4h/WQ) condition for a

constant aging time of 4h as a function of aging temperature.

Aging condition

Volume p

0.2% YS

(MPa)

True Fracture

strain

%RA

450 C 15.8% 1532 0.01 1.0

550 C 15.8% 1285 0.03 3.0

600 C 15.8% 1259 0.07 7.4

650 C 15.8% 1239 0.13 12.1

24

Figure 1: Microstructure of the rolled plate. The plate was soaked at 800°C for 1 hour and

rolled down to 15 mm thickness from 30 mm initial thickness. The heavy reduction has

resulted in breaking down even the grain boundary rains.

25

Figure 2: (a) Pseudo binary phase diagram of alloy showing all three solution treatment and

aging treatment. (b) A schematic of the different heat treatments carried out in the present

study on a time temperature plot.

(b)

1h 4h 8h 16h

26

Figure 3: Optical microstructure of

27

Figure 4 °C/1h/WQ) and aged specimen at

(a) 450°C/1h/AC and (b) 450°C/8h/AC (c) 550°C/1h/AC and (d) 550°C/8h/AC, showing the presence of

28

Figure 5: (a) The SAD pattern of [110] zone axis of -phase showing a number of diffracted spots other than that from phase. The existence of diffraction spot from is not clearly visible due to the presence of extra spots which are due to multivariants of Burger related phase. (b) A SAD pattern the specimen was tilted around (112), the presence of spots from could be distinctly seen at the 1/3rd and 2/3rd positions along (112) diffracted spot and transmitted beam as shown.

(a) (b)

29

Figure 6 treated (885°C/1h/WQ) and aged specimen at (a)

600°C/4h/AC (b) 650°C

the grain boundaries and almost two morphologies are also seen.

30

Figure 7: Electron back scatter micrographs of the alloy which has been imparted sufficient

coloured fine g

31

Figure 8: SEM micrographs of specimens + solution treated (a) 825°C/4h/AC and aged at 650°C/4h/AC

and (b) 800°C/4h/AC and aged at 650°C/4h/AC, showing the presence of fine globular primary phase

present at the grain boundaries as well as within the grains and uniformly distributed

throughout. Fine re-crystallised grains are observed and the volume higher at lower

i t t

32

-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

700

800

900

1000

1100

1200

1300

1400

1500

0.2

%Y

S (

MP

a)

650°C

600°C

550°C

Aging Time (h)

0.2

%Y

S (

MP

a)

Aging Time (h)

450°C

(a)

ST825

-2 0 2 4 6 8 10 12 14 16 18

-2

0

2

4

6

8

10

12

14

16

650°C

600°C

550°C450°C

% E

longation

Aging Time (h)

% E

longation

Aging Time (h)

(b)

Figure 9



aging time showing negligible elongation in case 450°C& 550°C and increase in elongation

at 600°C and 650°C for a given aging time.

33

-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

700

800

900

1000

1100

1200

1300

1400

1500

0.2

%Y

S (

MP

a)

650°C

600°C

550°C

Aging Time (h)

0.2

%Y

S (

MP

a)

Aging Time (h)

450°C

(a)

ST825

-2 0 2 4 6 8 10 12 14 16 18

0

2

4

6

8

10

12

14

16

18

20

22

650°C

600°C

550°C

450°C

Aging Time (h)

% E

longation

% E

longation

Aging Time (h)

ST825(b)

Figure 10:



aging time showing increase in ductility with increase in aging time at a particular

temperature.

34

-2 0 2 4 6 8 10 12 14 16 18

700

800

900

1000

1100

1200

1300

1400

1500

1600

1700

ST800

650°C

600°C

550°C

450°C

0.2

%Y

S (

MP

a)

0.2

%Y

S (

MP

a)

Aging Time (h)

Aging Time (h)

(a)

-2 0 2 4 6 8 10 12 14 16 18

0

5

10

15

20

25

650°C

600°C

550°C

450°C

Aging Time (h)

%E

longation

% E

longation

Aging Time (h)

(b)

ST800

Figure 11

of aging temperature and time (a) 0.2% yield strength vs. aging time showing constant

strength with increase in aging time for 450°C and 550°C and decrease in strength at higher

aging temperature and (b) % elongation vs. aging time showing increase in ductility with

increase in aging time at a particular temperature.

35

Figure 12:Fractographs of room temperature tensile tested specimen of Ti-5553 in

(885°C/1h/AC) condition showing (a) overall fracture surface, which appears ductile with a

few faceted features (b) magnified image showing shallow dimples.

36




faceted and intergranular feature on the facets. In some region secondary cracks are also seen

(shown by arrows).

37




faceted and intergranular feature on the facets.

38




faceted and intergranular features surrounded by shallow dimples.

39


(885°C/1h/WQ) and aged (650°C/4h/AC) condition (a) low magnification fractograph shows

mixed mode type of fracture and (b) high magnification fractograph showing faceted features

surrounded by fine and shallow dimples indicating a mixed mode fracture.

40

Figure 17: Fractographs of room temperature tensile tested specimen of Ti-5553 in

(825°C/4h/WQ) condition, showing (a) overall fracture area, which appears ductile and (b) magnified

image showing fine and deep dimples.

41

Figure 18: Fractograph of room temperature tensile tested specimens of Ti-5553 in

(825°C/4h/WQ) and aged (450°C/4h/AC) condition (a) low magnification fractograph

showing ductile failure mode and (b) high magnification fractograph showing fine dimples.

Some secondary cracks are also seen.

42


(825°C/4h/WQ) and aged (550°C/4h/AC) condition. SEM micrograph at (a) low

magnification and (b) higher magnification shows mixed mode of intergranular and ductile

fracture features. Ductile failure features are more prominent.

43


(825°C/4h/WQ) and aged (600°C/4h/AC) condition showing ductile fracture features at (a)

low magnification and (b) high magnification.

44


(825°C/4h/WQ) and aged (650°C/4h/AC) condition showing completely ductile failure mode

at (a) low magnification and (b) high magnification.

45

Figure 22:Fractographs of room temperature tensile tested specimen of Ti-5553 in

(800°C/4h/WQ) condition showing (a) overall fracture area, which appears ductile and (b) magnified

image showing deep dimples.

46


(800°C/4h/WQ) and aged (450°C/4h/AC) condition(a) low magnification showing ductile

failure mode and (b) high magnification showing fine dimples. Some secondary cracks are

also seen.

47

Figure 24: Fractograph of room temperature tensile tested specimens of Ti -

(800°C/4h/AC) and aged (550°C/4h/AC) condition showing predominantly ductile failure at

(a) low magnification and (b) high magnification. SEM micrograph shows mixed mode of

inter-granular and ductile fracture features at higher magnification. Ductile mode is more

prominent.

48


(800°C/4h/WQ) and aged (600°C/4h/AC) condition, showing completely ductile dimpled


49


ST2(800°C/4h/AC) and aged (650°C/4h/AC) condition, showing completely ductile dimpled


50

450°C 550°C 600°C 650°C

700

800

900

1000

1100

1200

1300

1400

1500

Aging Condition (X°C/1h/AC)

0.2

% Y

S (

MP

a)

0.2

% Y

S (

MP

a)


800°C/4hrs/WQ

825°C/4hrs/WQ

885°C/1hr/WQ

Breaking Strength(a)

450°C 550°C 600°C 650°C

0

5

10

15


% E

longation


% E

longation

(800°C/4h/WQ)

(825°C/4h/WQ)

(885°C/1h/WQ)

(b)

Figure 27 unction of aging



d then decreased (at 450°Cand

550°C, sample broken in elastic range) and (b) % elongation vs. aging condition


aging time.

51

450°C 550°C 600°C 650°C

800

900

1000

1100

1200

1300

1400

1500

1600


0.2

% Y

S (

MP

a)

0.2

% Y

S (

MP

a)


800°C/4hrs/WQ

825°C/4hrs/WQ

885°C/1hr/WQ

Breaking Strength

(a)

450°C 550°C 600°C 650°C

-2.5

0.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0


% E

longation

% E

longation


800°C/4hrs/WQ

825°C/4hrs/WQ

885°C/1/WQ

(b)

Figure 28



and 550°C, sample broken in elastic range)and (b) % elongation vs. aging condition


aging time.

52

450°C 550°C 600°C 650°C

800

900

1000

1100

1200

1300

1400

1500

1600


0.2

% Y

S (

MP

a)

0.2

% Y

S (

MP

a)


800°C/4hrs/WQ

825°C/4hrs/WQ

885°C/1hr/WQ

Breaking Strength

(a)

450°C 550°C 600°C 650°C

-2.5

0.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0


% E

lonagtion

% E

longation

Aging Conditon (X°C/16h/AC)

800°C/4hrs/WQ

825°C/4hrS/WQ

885°C/1hrs/WQ

(b)

Figure 29



and 550°C the sample broke in the elastic range) and (b) % elongation vs. aging condition

(X°C/16h/AC) showing increase in ductility with increase in aging temperature for given 16h

of aging time.

53

Figure 30: Plot of % elongation Vs 0.2% yield strength of Ti-5553 in all solution treatment

and aging condition investigated in this study. The encircled region represents optimum

combination of strength and ductility.

400 600 800 1000 1200 1400 1600

0

2

4

6

8

10

12

14

16

18

20

22

ST and aging treatment

ST and aging treatment

(800) ST and aging treatment

% E

LO

NG

AT

ION

0.2% YIELD STRENGTH (MPa)

54

Research Highlights Alloy was double melted in Vacuum Arc and then it was thermo-mechanically

processed. Microstructure was determined as a function of solution treatment and aging (STA).

Effect of solution treatment and aging on microstructure and tensile properties of high strength β...

Documents

Transcript of Effect of solution treatment and aging on microstructure and tensile properties of high strength β...