Papers by Author: Jing Fu Liu

Abstract: In this paper, Ti(C,N)-Based cermets with addition of nano-carbides were fabricated by conventional powder metallurgy techniques. Then the mechanical properties, microstructure and corresponding formation mechanism have been investigated. According to the results, the microstructures of sintered cermets are composed of three kinds of hard grains: one with black core/grey shell, one with white core , and the other with no core. In addition, with more nano-carbides adding, the number of white core grains increases and that of black core grains decreases. It is also found that sintered cermets with nano-carbide additions exhibit higher transverse rupture strength and higher hardness than the others originated from much finer and more homogeneous microstructure. However, cermets with nano-micro carbide additions show the most poor mechanical properties among all sintered cermets, including conventional cermets, due to the obviously heterogeneous microstructure. And this can be explained by Ostwald ripening theory.

Abstract: Laser welding of 1A90 pure aluminum and ZL114A aluminum alloy with powder under the same laser welding parameters were carried out in this work. The relation between weld elements and solidification cracking formation of these two materials was investigated in the perspective of metallurgical factor. And the alloy element contents and distribution near the cracks were determined by scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS). Then the concept of weld element equivalent was introduced comparing with the carbon equivalent expression. The weld element equivalent expressions were established by using mathematics regress. And the verified results indicate that the weld element equivalent expressions can properly forecast the formation of solidification cracking.

Abstract: To analyze the feasibility about diffusion bonding of Ti-6Al-4V alloy (represented by TC4 below) and type 25 low carbon steel (represented by 25-steel below), two kinds of experiments have been conducted by Gleeble-1500. One is directly diffusion bonding research of TC4 and 25-steel, the other is diffusion bonding of TC4 and 25-steel with adding Ni intermediate layer. The surface microstructures and the phase composition of bonding Joint have been systematic analysis through scanning electron microscope (SEM), energy spectrometer and XRD. Results indicated that the Ni intermediate layer largely improve the strength of joints observably, by suppressing the harmful diffusion between two sorts of based metal to avoid the appearance of harmful intermetallics in the joints.