Effect of Gas Composition on Nitriding and Wear Behavior of Nitrided Titanium Alloy Ti-15V-3Cr-3Al-3Sn
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JMEPEG (2013) 22:2623–2633 DOI: 10.1007/s11665-013-0540-0
Effect of Gas Composition on Nitriding and Wear Behavior of Nitrided Titanium Alloy Ti-15V-3Cr-3Al-3Sn C. Anandan, P.Dilli Babu, and L. Mohan (Submitted November 8, 2012; in revised form December 26, 2012; published online April 6, 2013) Titanium alloy, Ti-15V-3Cr-3Al-3Sn was nitrided at different temperatures with low pressure plasma with 100% nitrogen, and nitrogen diluted with hydrogen and argon. The nitrided layers were characterized for hardness, structure, and composition. Nitrided samples show weight gain that depended on temperature and duration of nitriding. EDS results show that intake of nitrogen is significant at temperatures above 750 °C. Hydrogen dilution increases intake of nitrogen. Samples nitrided with hydrogen dilution have lower surface roughness and higher nitrogen concentration. Depth profiling by XPS shows the formation of nitride in the near-surface region and also that nitrogen concentration in the interior of the nitrided layers is higher at higher temperatures. Micro Raman shows that formation of nitride takes place at higher temperatures. XRD shows that the nitrided layers consist predominantly of alpha Ti and Ti2N. This is reflected in the hardness increase and hardness profile in the nitrided samples. The low intake of nitrogen by the alloy is attributed to the low solubility of nitrogen in beta alloy and low diffusion coefficient of nitrogen. Reciprocating wear studies showed a lower coefficient of friction and lower wear loss for nitrided samples compared to that of substrate.
Keywords
gas dilution, hardness, plasma nitriding, Ti-15-3, titanium alloy, wear, XPS
1. Introduction Titanium and its alloys have high strength-to-weight ratio and possess excellent corrosion resistance. Pure Titanium is an a alloy, and the a-to-b transformation occurs at about 885 C. Depending on the nature of alloying elements and their concentration, titanium alloys can exist in a, b, or a + b form, and the transformation temperature may be higher or lower than pure titanium (Ref 1). In case of a + b alloy, Ti-6Al-4V, the a-to-b transformation occurs at 980 C. On the other hand, beta alloys are a class of alloys for which the transus temperature can be as low as 750 C (Ref 1, 2). Most of the metal-forming operations of the titanium alloys are performed at high temperatures because of the high temperatures needed for inducing plastic flow. However, these high temperatures are energy intensive. Also these thermomechanical treatments may induce unwarranted metallurgical changes in the base material. The low beta transus temperature of titanium alloys make them amenable to lower-temperature operations compared with a + b alloys. Among the several b alloys, vanadium-containing alloys such as Ti-10-2-3 and Ti-15-3—find prominent place in aerospace sector. For example, Ti-10-2-3 has been used in landing gear application in aircraft and Ti-15-3 has found several applications in aerospace industry (Ref 2). C. Anandan, P. Dilli Babu, and L. Mohan, Surface Engin
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