Wear behavior of high entropy alloys containing soft dispersoids (Pb, Bi)

Abstract

Intrinsic high entropy alloys (HEAs) exhibit superior mechanical properties (hardness, strength, ductility, toughness etc.) and hence, they are considered as potential candidates for wear resistance applications. Wear resistance of HEAs can further be improved by engineering microstructure using various novel design concepts. One of such concepts involves the usages of soft dispersoids (Sn, Pb, Bi, Sb etc.) in the HEA matrix. However, the challenge is to engineer the novel microstructure consisting of soft dispersoids, dispersed uniformly in the HEA matrix, using suitable processing techniques. In this connection, the present work reports the effect of soft dispersoids, such as Pb and Bi on the wear behavior in equiatomic CuCrFeTiZn and AlCrFeMnV HEAs. The alloys containing Pb and Bi were synthesized using mechanical alloying (MA) followed by spark plasma sintering (SPS) in inert argon atmosphere. Phases and microstructure of milled powder and sintered alloys were investigated using XRD, SEM equipped with EDS. Sliding wear tests were also carried out for all the sintered samples at 2N, 5N, 7N and 10N load for various sliding speeds. Wear results indicate coefficient of friction (COF) does not vary much with varying the Pb concentration in HEAs. However, wear rate decreases significantly with increasing the Pb content in the alloys. For HEAs containing Bi, there is considerable decrease in the COF as well as in the wear rate even for a lower (5%) Bi content. Increasing load does not cause any change in the COF in both cases. However, wear rate decreases substantially due to increase of load. In addition, SEM analysis of the worn surface and wear debris were performed and it has been found that oxidative wear is the dominant wear mechanism in these systems. However wear tracks indicate the presence of abrasive wear. Analysis of Raman spectroscopy of wear debris confirms the presence of Fe2O3, Bi2O3 and PbO.