Microstructure evolution, wear behavior, and corrosion performance of alloy steel gradient material fabricated by direct laser deposition
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T
Authors: Jiang, P. F.; Zhang, C. H.; Zhang, S.; Zhang, J. B.; Chen, J.; Liu, Y.
In this paper, the corrosion-wear-resistant alloy steel gradient material for camshaft was successfully prepared by direct laser deposition (DLD). The phase evolution, microstructure characteristics, microhardness, wear behaviors and corrosion resistance of alloy steel gradient material were studied using X-ray diffraction (XRD), electron backscatter diffraction (EBSD), hardness tester, wear tester and electrochemical workstation, respectively. The results showed that phase evolutions with the increase of stainless steel powders from alpha-Fe + Cr23C6 to a-Fe + Cr23C6 + (Cr, Fe)(7)C-3. The microstructure of the alloy steel gradient material was refined with increasing the stainless steel powders. The preferred texture was weak with the increase of gradient due to the each layer experiencing a variety of complex thermal cycle effects. Meanwhile, the content of high-angle grain boundaries (HAGBs) and the volume fraction of Cr23C6 and (Cr, Fe)(7)C-3 increased with gradient increasing, which promoted the toughness and enhanced the wear reaiatance of the material. In addition, the microhardness distribution of alloy steel gradient material showed a gradient increase from 281 HV to 795 HV along with deposition direction. The wear resistance and corrosion resistance of alloy steel gradient material were extremely improved. The average specific wear rate and corrosion current density of alloy steel gradient material specimen were 0.30 x 10(-5) mm(3)/Nm and 1.3 x 10(-7) A cm(-2), respectively. (C) 2020 The Author(s). Published by Elsevier B.V.
Optimizing the microstructure and mechanical behaviors of bimodal Mo-Si-B alloy by heat treatment
INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS
Authors: Li, Rui; Chen, Xuan; Li, Bin; Wang, Juan; Wang, Tao; Yan, Fuxue; Zhang, Guojun
Previous studies revealed that developing bi-modally structured alpha-Mo grains in the fine-grained Mo-12Si-8.5B-0.57 wt% La2O3 alloy could improve room-temperature fracture toughness without sacrificing strength dramatically. However, the toughness is expected to be enhanced further for engineering application of alloy. Here, the optimization of the bimodal alpha-Mo microstructure was achieved by annealing treatment at 1700-1800 degrees C. After annealing, the semi-continuous or isolated alpha-Mo colonies were transformed into the continuous alpha-Mo matrix meanwhile the volume fraction of alpha-Mo was improved slightly. Besides, the fine-grained and coarse-grained regions were coarsened concurrently and the distribution of them became more homogenous. The 1800 degrees C-annealed bimodal alloy exhibited an optimal microstructure consisting of dispersive Mo3Si/Mo5SiB2 (similar to 1.72-2.00 mu m) particles distributed in a continuous bimodal fine-grained (similar to 2.03 mu m)/coarse-grained (similar to 6.36 mu m) alpha-Mo matrix. Also, this alloy presented a significantly improved fracture toughness (13.41 MPa.m(1/2)) and high compression strength (2682 MPa) and hardness (841 HV) simultaneously. Toughening mainly originated from crack trapping in the coarsening bimodal alpha-Mo structure and forming intragranular micro-cracks in the coarsening alpha-Mo and intermetallic phases induced by La2O3. High compression strength was attributed to the coarseness of alpha-Mo phase improving the plastic deformation capacity of alloy.