Abstract
The tribological behaviors of Ti-Ni51.5 at% alloy strengthened by finely dispersed Ni4Ti3 particles in reciprocating sliding against GCr15, Al2O3, and ZrO2 at room temperature were studied. Interestingly, the coefficient of friction (COF) suffered a sheer drop (from 0.9 to 0.2) when the aged alloy slid against GCr15 at a frequency of 20 Hz under a 20 N load without lubrication. However, severe-mild wear transition disappeared when a solutionized alloy was used. Moreover, the COF stabilized at a relatively high level when Al2O3 and ZrO2 were used as counterparts, although their wear mechanisms showed signs of oxidation. Scanning electron microscopy (SEM) and X-ray element mappings of the wear scars of the counterparts clearly indicate that the formation of well-distributed tribo-layer and material transfer between the ball and disk are pivotal to the severe-to-mild wear transition in the aged Ti-Ni51.5 at% alloy/GCr15 friction pair. The higher microhardness and superelasticity of the aged alloy significantly accelerate the material transfer from GCr15 to the disk, forming a glazed protective tribo-layer containing Fe-rich oxides.
Highlights
TiNi-based shape-memory alloys (SMAs) have been widely applied in several industries owing to their excellent shape memory behaviors and superelasticity (SE) [1]
The results of differential scanning calorimeter (DSC) show austenite start (As) = 29.4 °C and martensite start (Ms) = –31.1 °C in the aged alloy, and Ms is below –120 °C in the solutionized alloy, which illustrates that the matrix of both alloys will be in the B2 state before the wear test at room temperature
1) The aged Ti–Ni51.5 at%/GCr15 couple under dry sliding shows clear signs of a severe-mild transition under a load of 20 N, stroke of 1 mm, and frequency of 20 Hz, but this transition disappears when it is lubricated with PAO10 or when the counterpart is replaced by an Al2O3 or ZrO2 counterpart
Summary
TiNi-based shape-memory alloys (SMAs) have been widely applied in several industries owing to their excellent shape memory behaviors and superelasticity (SE) [1]. Their potential SE adds to the combination of high coefficient of friction (COF) and an impressive wear resistance, which incites researchers to investigate them as wear-resistant materials [2−5]. The existing studies on the tribological applications of TiNi SMAs primarily illustrate the influence from the microstructure and experimental conditions on its tribological behaviors, e.g., phase states [6], grain size [2], temperature [7], and loading [8].
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