Novel gradient alloy steel with quasi-continuous ratios fabricated by SLM: Material microstructure and wear mechanism

Highlights: • The first attempt is made to prepare a quasi-continuous ratio gradient alloy steel by SLM. • With the increase of wear-resistant stainless steel content, the grain size decreases obviously. • The external layer of gradient alloy steel has the best wear resistance, and the wear rate is about 34.8% of the matrix. • A micro wear model is established to comprehend the wear mechanism of SLMed materials better. In this work, a quasi-continuous ratio gradient alloy steel with a 24CrNiMo matrix for high-speed railway brake discs is prepared by selective laser melting (SLM). The composition of sample is x% 24CrNiMo + (1-x)% wear-resistant stainless steel (x is 100, 65, 35 and 0). The relationship between the microstructure and wear resistance of the samples is thoroughly investigated by electron back-scatter diffraction (EBSD) and friction-wear tester. The results show that the grains of samples prepared by SLM can be roughly divided into three types, which correspond to different wear mechanisms according to their growth characteristics. When x is 0, the sample has the finest grains, the smallest Schmidt factor value, the maximum content of low-angle grain boundaries and strengthening phase, corresponding to the optimum wear rate and coefficient of friction (COF) of 7.46 × 10⁻⁵ mm³/N m and 0.31, respectively and the wear rate is about 34.8% of the matrix. A micro-wear mechanism analysis model is established to display the micro wear process of SLM samples.