Metodología

Miniature specimen testing is attempted using Gleeble 3800 system. Miniature specimens and fixtures are fabricated from the XM-19(UNS S20910) material using EDM wire cut technique. Miniature specimen is having thickness of 1mm and length of 14mm. Specimen is tested at 200°C temperature and 0.01 of strain rate. Controlled Heating of miniature size specimen is the challenging part of these experiments. Parallel heating technique is used for controlled heating of the specimen.

Figure 15 shows the tensile tested miniature specimen. Figure 16 shows the programmed temperature and controlled heating of the specimen. Measured UTS of the XM-19 specimen is 592MPa at 200°C as shown in fig. 17.

Fig. 15: Tensile tested miniature size specimen

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Fig. 16: Heating Cycle of Miniature Specimen

Fig. 17: Stress Strain Plot for XM 19 material at 200°C

CONCLUSION

Pure tungsten sintering experiments are performed using Gleeble 3800 systems. Maximum 93.50% of theoretical density is achieved of sintered pallet. Future work will be focused on optimization of the sintering fixture and sintering parameters to achieve higher densification of tungsten material with desired properties. Dissimilar material joining experiments were performed successfully by diffusion bonding and vacuum brazing methods. Diffusion bonding parameters like pressure, temperature and holding time are the crucial parameter to

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define the sound joint between two dissimilar materials. Optimization of the process parameter for diffusion bonding and vacuum brazing is an ongoing works.

Thermal fatigue cycle experiments are successfully performed as per the operation requirements of different specimens. Tungsten tensile tests are performed at various temperature of 400C-1200°C. It is found that for temperature above 600°C, tensile tests are performed successfully. Tensile test at 400°C remains failed as specimen broken down from the pin region in grip contacts. Miniature specimen testing using Gleeble 3800 system is attempted. Miniature specimen is successfully tested at 200°C temperature.

ACKNOWLEDGEMENT

The authors are sincerely thankful to Mr. Jainish Topiwala and Mr. Hitesh Patel for their contribution in conducting thermal fatigue tests of EB welded CuCrZr material specimen.

The authors are thankful to Dr. Charulata Dubey for her contribution in conducting tungsten tensile tests. The authors are also thankful to ARCI, Hyderabad for providing the Tungsten coated samples to carry out thermal fatigue experiments.

REFERENCES

[1]. G. Partheepan, D.K. Sehgal, et al. “Finite Element Application to Estimate In-service Material Properties using Miniature Specimen” International Journal of Aerospace and Mechanical Engineering 2:2 2008

[2]. Sunil Goyal, V. Karthik, et al. “Finite element analysis of shear punches testing and experimental validation” Materials and Design 31 (2010) 2546–2552

[3]. V. Karthik, P. Visweswaran, et al. “Tensile–shear correlations obtained from shear punch test techniqueusing a modified experimental approach” Journal of Nuclear Materials 393 (2009) 425–432

[4]. Avijit Mondal, Anish Upadhyaya “Effect of heating mode on sintering of tungsten” Int.

Journal of Refractory Metals and Hard Materials 28 (2010) 597–600

[5]. Small Specimen Test Techniques - 5^th Volume – Journal of ASTM international special technical publication STP1502

[6]. Powder Metallurgy: Science, Technology, and Materials – Anish Upadhyaya, G.S.

Upadhyaya

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[7]. Charu Lata Dube, Alpesh Patel, et al. “High Temperature Tensile Properties of Tungsten” 1^st International conference on structural integrity – ICONS 2014

[8]. K.P Singh, Alpesh Patel, et al. “Study the Effect of Thermal Cyclic On SS316L to CuCrZr Brazed Joint” 29th National Symposium on Plasma Science & Technology (PLASMA 2014)

[9]. Shailesh Kanpara, G. Sivakumar, et al. “Development of Tungsten Coating using Atmospheric Plasma Spraying for First Wall Applications in Fusion TOKAMAK” 6^th Asian Thermal Spray Conference (ATSC-2014)

[10]. K.P Singh, S.S Khirwadkar, et al. “Studies for The Optimization Of Brazed PFC Using Coupon Based Samples” 27th National Symposium on Plasma Science & Technology (PLASMA 2012)

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Austenitic stainless steels are extensively used in many areas of application because of their superior corrosion resistance and satisfactory mechanical properties. Amongst various grades of stainless steel, titanium stabilized SS 321 is chiefly used for high temperature structural application due to its extraordinary stability against sensitization at higher temperature. Titanium tends to form carbides/carbonitrides, thereby reducing the carbon content in the austenitic matrix. This helps preventing sensitization problem. The stability of austenitic phase at room temperature is key factor to govern the propensity of strain induced martensitic transformation during cold deformation of austenitic stainless steels. Titanium is a strong ferrite stabilizer. The effect of dissolved titanium content in austenite/ the percentage precipitation of titanium on the stability of austenite were studied.

Solutionized and as-received specimens were considered for experiments. Solutionizing was done at 1100⁰C for 30 mins and then water quenched. One of the solutionized specimens was heated at a slow rate of approx. 5⁰ C/minute from room temperature to 1100⁰C, while the other one was rapidly heated upto the solutionizing temperature. As received structure showed austenitic matrix along with coarse titanium carbide precipitates.

Tensile tests on samples were carried out and the volume percentage of the strain induced martensite in each specimen was estimated with a calibrated ferritscopic measurement. Optical microscopy, SEM and EDAX were also performed to find out grainsize, morphology and composition of titanium rich precipitates and regions of austenitic matrix. The results showed a higher propensity of strain induced martensitic transformation in case of solutionized samples. The effect of strain rate on the transformation was also realized through carrying out tensile tests at different strain rates on as received specimens. A faster test was seen to hinder martensitic transformation, quite expectedly, possibly because of adiabatic heating.

Keywords: Austenitic stainless steel, Titanium, Strain Induced Martensite

INTRODUCTION

Austenitic stainless steels are used in wide range of applications for their superior corrosion resistance and acceptable formability. AISI 321 grade has titanium carbide precipitates on austenitic matrix, which provides high temperature resistance to sensitization problems. For manufacturing structural parts with complex geometry, it is imperative to predict the