DR B R AMBEDKAR NATIONAL INSTITUTE OF TECHNOLOGY JALANDHAR-144011, INDIA

DEPARTMENT OF INDUSTRIAL AND PRODUCTION ENGINEERING6th INTERNATIONAL CONFERENCE ON PRODUCTION AND INDUSTRIAL

ENGINEERING (CPIE-2019)

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF LAMELLAR ABSAnil Kumar Singla1, Jagtar Singh2, Vishal S Sharma3

1-2 Department of Mechanical EngineeringSant Longowal Institute of Engineering and Technology, Longowal-148106, INDIA

3 Department of Industrial and Production EngineeringDr B R Ambedkar Natrional Institute of Technology Jalandhar-144011, INDIA

ABSTRACT(A4 sheet size with 2.54 cm margines all over with single spacing, Times New Roman font with 12 point scale, Title to be all Caps and Bold, Tables in Arial with 8 point scale, Maximum number of pages is 6, Reference Style MathPhysSci, Citation Style Numbered and Numbering Style, sample is attached )Titanium and its alloys especially Ti-6Al-4V and its ELI grade exhibit a unique combination of mechanical, physical and corrosion resistance properties, which have led to their desirable response for critical and demanding aerospace, industrial, chemical, medical and energy industry services. The mechanical properties of Ti-6Al-4V ELI can be altered significantly when subjected to different heat treatment cycles. β annealing of Ti-6Al-4V is one such heat treatment that finds extensive applications in industry. β annealing leads to formation of lamellar microstructure that has many desirable mechanical properties. In his work microstructure and mechanical properties of lamellar Ti-6Al-4V ELI have been investigated.

NOMENCLATUREHT: Heat TreatmentGQ: Gas QuenchedELI: Extra Low InterstitialASTM: American Society for Testing and Materials VHT: Vacuum Heat TreatmentEDM: Electro Discharge MachiningVHN: Vicker Hardness NumberMA: Mill Annealed Ys: Yield strengthUts: Ultimate tensile strength

1. INTRODUCTION Titanium is the fourth most abundant structural metals after aluminium, iron, magnesium and ninth most plentiful element [1,2]. Titanium is available as commercially pure and as alloys. These alloys are usually divided into three categories alpha (α), alpha-beta (α+β) and beta (β). The α+β alloys, the most widely used alloy group, contain one or more α stabilisers plus one or more β stabilisers. Amongst the α+β alloys, Ti-6Al-4V and its variants are by far the most popular titanium alloys and constitute more than 50% of all titanium alloy applications [1]. In this work MA Ti-6Al-4V ELI titanium alloy has been subjected to HT above beta transus using vacuum hardening furnace. It was followed by aging treatment. The microstructure and mechanical properties of MA and β annealed titanium alloy have investigated and compared.

2. EXPERIMENTATION

2.1 Material

1

The raw material selected for the present research work was Ti–6Al–4V ELI titanium alloy. According to elemental analysis of as received raw material, its chemical composition was 0.01% C, 0.04% Fe, 0.08% O, 3.9% V, 5.9% Al and balance Ti.

2.2 Specimen PreparationTi-6Al-4V ELI is very reactive alloy and requires special attention during specimen preparation. Due care has been taken to avoid any deformation and overheating. Sectioning of Ti-6Al-4V ELI titanium alloy has been done on Struers Labotom-5 (manual cutting machine).

2.3 Heat TreatmentLamellar microstructure and their variants generally cover most of the applications of Ti-6Al-4V ELI alloy. These microstructures are attainable by carrying out heat treatment in the β field near to beta transus. Heat treatment in the β field is also focus of many investigations in the past [3-9]

Figure 1. Vacuum Hardening Furnace

Figure 2. HT cycle

0 0.5 1 1.25 1.5 2 2.5 3 3.5 4Time (hrs.)

RT

200

400

600

9801035

1200

Tem

pera

ture

(o C)

Beta Transus

Beta Annealing

AgingGQ

AC

2.4 Tensile PropertiesTensile test has been carried out on UTM, capacity 200 Ton, Model No.WAW-1500H at Institute of Auto Parts & Hand Tools Technology, Ludhiana. ASTM standards E8 [11] has been followed for the test. Threaded specimen has been used to avoid slippage during the test.

DR B R AMBEDKAR NATIONAL INSTITUTE OF TECHNOLOGY JALANDHAR-144011, INDIA

DEPARTMENT OF INDUSTRIAL AND PRODUCTION ENGINEERING6th INTERNATIONAL CONFERENCE ON PRODUCTION AND INDUSTRIAL

ENGINEERING (CPIE-2019)

2.5 Charpy Impact strength and MicrohardnessTest for charpy impact strength has been carried out on Impact Test Machine 2J Make FIE, India at Institute of Auto Parts & Hand Tools Technology, Ludhiana. ASTM standard E23 [10] has been followed for the test. V-notch has been cut using wire EDM EXCETEK S & T, at Sant Longowal Institute of Engineering and Technology (SLIET), Longowal. Test for Microhardness has been done on MVH-II, OMNITECH, India at SLIET, Longowal. ASTM standard E384 [12] has been followed for the test. Specimens for microhardness and optical microscopy have been cut from longer bar after VHT. The diameter and thickness of the specimens is 15 mm and 5mm respectively. Wire EDM has been used for specimen cutting.

2.6 Optical MicroscopyOptical Microscopy has been used for cross section metallography. It is an established procedure for visualisation of microstructure. Inverted Trinocular Metallurgical Microscope has been used for optical microscopy. Analysis of the micrographs has been done using QSMIAS 4.0 (Metallurgical Image Analysis System) software.

3. RESULTS AND DISCUSSIONS3.1 Tensile PropertiesThree specimen both for MA and β annealed lamellar Ti-6Al-4V ELI have been tested for Ys, Uts, %age elongation and %age RA. The average tensile values for MA and β annealed Ti alloys are shown in Table 1.

Table 1. Tensile properties of MA and β annealed Ti-6Al-4V ELISpecimen Ys (MPa) Uts (MPa) %age elongation %age RAMA 959 1039 18.5 57β annealed (Lamellar) 921 934 7.22 13

Ys and Uts have been decreased by 4.12% and 11.24% respectively after β annealing. Correspondingly %age elongation and %age RA have been reduced for lamellar microstructure as compared to MA. The neck formation has been significantly reduced due to formation of lamellar microstructure.

3.2 Hardness and Charpy StrengthVickers Microhardness has been tested at five different locations for both MA and β annealed Ti alloys. The results of microhardness are shown in Table 2.

Table 2. Microhardness of MA and β annealed Ti-6Al-4V ELISpecimen Microhardness value (VHN) Average

Microhardness (VHN)

Location 1 Location 2 Location 3 Location 4 Location 5

MA 304 327 332 309 296 313.6β annealed (Lamellar)

335 346 337 341 344 340.6

Three specimen of both MA and β annealed Ti alloys have been tested for charpy impact strength. The average value of charpy impact strength for MA specimen is 25J while for β annealed lamellar Ti-6Al-4V ELI is 32J. Microhardness and charpy impact strength have been increased by 8.6% and 28% respectively for lamellar microstructure as compared to MA. The enhancement in hardness and charpy impact strength can be attributed to formation of lamellar microstructure.

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3.3 Optical MicrographsThe optical micrographs of MA and β annealed lamellar Ti-6Al-4V ELI are shown in Figure 3(a) and Figure 3(b) respectively. MA Ti-6Al-4V ELI alloy constitutes equiaxed microstructure. Microstructure consists of α phase (bright region) and β phase (dark region). The β phase is appearing on the boundaries of equiaxed α grains. The α phase and β phase are clearly indicated in the optical micrographs (refer Figure 3(a)). The same microstructure of MA Ti-6Al-4V ELI has also been reported in [13]. The uniform distribution of α phase and β phase make the material more ductile. This leads to increase in tensile strength values, %age elongation and %age RA. However, the microhardness and charpy impact strength are lower as compared to β annealed microstructure.

Figure 3(a). 1000x optical micrograph of MA Ti-6Al-4V ELI

Figure 3(b). 1000x optical micrograph of Lamellar Ti-6Al-4V ELI

4. CONCLUSIONSβ annealing of Ti-6Al-4V ELI has been done and its mechanical properties and microstructure has been investigated and compared with that of MA Ti alloy. Following conclusions have been drawn from the study.

Lamellar (plate like) microstructure has been formed upon β annealing of Ti-6Al-4V ELI that is significantly different as compared to microstructure of MA Ti alloy.

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6. Moustahfid, H., Gey, N., Humbert, M and Philippe, M, J.:Study of the β-α phase transformations of a Ti-64 sheet induced from a high-temperature  β state and a high-

DR B R AMBEDKAR NATIONAL INSTITUTE OF TECHNOLOGY JALANDHAR-144011, INDIA

DEPARTMENT OF INDUSTRIAL AND PRODUCTION ENGINEERING6th INTERNATIONAL CONFERENCE ON PRODUCTION AND INDUSTRIAL

ENGINEERING (CPIE-2019)

temperature α + β state. Metallurgical and Materials Transactions A. 28(1), 51-61 (1997).

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9. ASTM E23: Standard Test Methods for Notched Bar Impact Testing of Metallic Materials. www.astm.org/Standards/E23

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11. ASTM E384: Standard Test Method for Microindentation Hardness of Materials. www.astm.org/Standards/E384

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