Micromechanical and tribological characterizations of high wear resistant superelastic titanium nickel shape memory alloy.

摘要

TiNi alloy has attracted great attention in recent years due to its superelasticity (SE) and shape memory effect (SME). It has been established that the superelastic or "pseudoelastic" effect of TiNi alloy is related to a reversible martensitic transformation, i.e., stress induced transformation. The high elastic recovery of TiNi alloy has made it a potential candidate for high wear resistance applications. However, the wear behavior of superelastic TiNi alloy is not well understood and more work is needed to be able to fully exploit its wear properties for tribological applications.;In the present study two types of commercially-obtained TiNi alloys were investigated, with austenite finishing temperatures at 18°C and -18°C, respectively. Ni, Ti and AISI 304 stainless steel plates were also tested for comparison. Dry sliding wear and friction tests, at selected ranges of normal loads, sliding speeds and testing temperatures were conducted using a ball-on-disc type configuration. Mechanical characterizations of materials were also performed, using tensile and nanoindentation tests. It has been found that although AISI 304 stainless steel and superelastic TiNi alloy have similar hardness, TiNi exhibits superior wear resistance. The wear rate of AISI 304 stainless steel is 5 to 20 times higher than TiNi and the coefficient of friction of AISI 304 stainless steel is twice as high as TiNi. The superior wear resistance of TiNi is attributed to low E/H ratio, high elastic recovery ratio and larger contact area. The E/H ratio of AISI 304 stainless steel is 4.5 times higher than TiNi; TiNi shows an up to 38% elastic recovery ratio which is 5 times higher than AISI 304 stainless steel and 3 times higher contact area than AISI 304 stainless steel. Furthermore, yield load of TiNi under a spherical indenter and a 40 N normal load is 11 times higher than that of AISI 304 stainless steel under the same conditions. The wear rates of TiNi and AISI 304 stainless steel both increase with normal load and decrease with testing temperature. The morphologies of worn surfaces after ball-on-disc tests were examined using SEM and EDS. The dominant wear mechanisms observed for TiNi were adhesion, abrasion and delamination, while those for AISI 304 stainless steel were adhesion and heavy plastic deformation. Under a higher working temperature (250°C), oxide forms, which enhances the wear resistance of both TiNi and AISI 304 stainless steel. The wear tracks of TiNi and AISI 304 stainless steel from scratch tests were investigated via AFM. AISI 304 stainless steel shows a significantly deeper and wider scar than TiNi. The average depth of the wear track of AISI 304 stainless steel is 8 times deeper than TiNi.