Joining mechanism of Ti/Al dissimilar alloys during laser welding-brazing process

Selective laser melting of TiC/Ti bulk nanocomposites: Influence of nanoscale reinforcement

It is generally believed that cracks in metal matrix composites (MMC) parts manufacturing are crucial to the reliable material properties, especially for the reinforcement particles with high volume fraction. In this paper, WC particles (WC p ) reinforced Fe-based metal matrix composites (WC p /Fe) were manufactured by laser melting deposition (LMD) technology to investigate the characteristics of cracks formation. The section morphology of composites were analyzed by optical microscope (OM), and microstructure of WC p , matrix and interface were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), in order to study the crack initiation and propagation behavior under different laser process conditions. The temperature of materials during the laser melting deposition was detected by the infrared thermometer. The results showed that the cracks often appeared after five layers laser deposition in this experiment. The cracks crossed through WC particles rather than the interface, so the strength of interface obtained by the LMD was relatively large. When the thermal stress induced by high temperature gradient during LMD and the coefficient of thermal expansion mismatch between WC and matrix was larger than yield strength of WC, the cracks would initiate inside WC particle. Cracks mostly propagated along the eutectic phases whose brittleness was very large. The obtained thin interface was beneficial to transmitting the stress from particle to matrix. The influence of volume fraction of particles, laser power and scanning speed on cracks were investigated. This paper investigated the influence of WC particles size on cracks systematically, and the smallest size of cracked WC in different laser processing parameters was also researched.

Crack initiation and propagation behavior of WC particles reinforced Fe-based metal matrix composite produced by laser melting deposition

A novel Selective Laser Melting (SLM) process was applied to prepare bulk-form TiC/Ti 5 Si 3 in-situ composites starting from Ti/SiC powder system. The influence of the applied laser energy density on densification, microstructure, and mechanical performance of SLM-processed composite parts was studied. It showed that the uniformly dispersed TiC reinforcing phase having a unique network distribution and a submicron-scale dendritic morphology was formed as a laser energy density of 0.4 kJ/m was properly settled. The 96.9% dense SLM-processed TiC/Ti 5 Si 3 composites had a high microhardness of 980.3HV 0.2 , showing more than a 3-fold increase upon that of the unreinforced Ti part. The dry sliding wear tests revealed that the TiC/Ti 5 Si 3 composites possessed a considerably low friction coefficient of 0.2 and a reduced wear rate of 1.42 × 10 − 4  mm 3 /Nm. The scanning electron microscope (SEM) characterization of the worn surface morphology indicated that the high wear resistance was due to the formation of adherent and strain-hardened tribolayer. The densification rate, microhardness, and wear performance generally decreased at a higher laser energy density of 0.8 kJ/m, due to the formation of thermal cracks and the significant coarsening of TiC dendritic reinforcing phase.

Selective Laser Melting of in-situ TiC/Ti5Si3 composites with novel reinforcement architecture and elevated performance

The carck-free Fe-based +20 wt% WC coating with large area was produced by mutli-track overlapping laser induction hybrid rapid cladding. The results showed that the maximum laser scanning speed and the maximum feeding rate of powder can be increased to 3500 mm/min and 120 g/min, respectively. The cast WC particles were dissolved almost completely and had a worse wettability with Fe-based metal matrix. The precipitated carbides such as M 12 C and M 23 C 6 (M=Fe, W, Cr) formed an intergranular network around the primary Fe-based phase enriched with tungsten. The microhardness of coating decreased first, and then increased slightly with an increase in the track. The first track had the highest microhardness (i.e. 870HV 0.2 ). Moreover, the wear weight of coating approximately had a linear relationship with the sliding distance, and increased with an increase in the sliding speed. The wear rate approximately remained constant with an increase in the sliding distance and was two times lower than that of the hardened steel AISI 1045 with a hardness of 60HRC. The wear mechanism during the dry sliding wear was a combination of oxidation wear and abrasion wear.

Microstructure and wear resistance of Fe-based WC coating by multi-track overlapping laser induction hybrid rapid cladding

Laser melt injection (LMI) was used to produce WC particles (WCp) reinforced metal matrix composites (MMCs) layer on the mild steel. During the LMI process, different parameters were applied, and the processing window of this technique was obtained. The MMCs layers were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The SEM result reveals that none macro-defects except few pores can be found in the MMCs layer, and the WCp distribute uniformly in the layer. In addition, some new phases can be found in the MMCs layer, where Fe3W3C is the predominant phase. At the same time, the amount of dissolved WCp plays a key role in the microstructure of the MMCs layer. The WC particle dissolved into the melt pool leads to the appearance of reaction products in the matrix, such as various primary Fe3W3C dendrites, and the liquid WC remained on the solid WC particle results in the formation of a thicker reaction layer.

WCp/Fe metal matrix composites produced by laser melt injection

Electron microscopy study of reaction layers between single-crystal WC particle and Ti–6Al–4V after laser melt injection

The laser melt injection (LMI) process was explored to produce WC particles (WCp) reinforced Ti–6Al–4V metal matrix composites (MMC). In particular monocrystalline WC powder was used as injection particles to avoid the intercrystalline cracking often observed in granular or cast WCp reinforced MMC. WCp were injected into the extended part of the melt pool just behind the laser beam. The process allowed for the minimization of the WCp dissolution caused by the direct irradiation of the laser beam, and the decomposition reaction between WCp and Ti melt. Different parameters were applied, and a processing window of LMI was obtained. WCp exhibit a graded distribution along the depth direction of the MMC layer. New phases such as TiC and W2C are observed in the MMC layer, in which TiC is the predominant phase. TiC grains present a continuous decrease in both amount and size with the distance from the surface to the bottom of the MMC layer. Two types of reaction layers around WCp can be distinguished, namely an irregular reaction layer and a cellular reaction layer. The growth and final morphology of reaction layers are most likely being dominated by the composition of the neighbouring melt pool. A gradual hardness distribution in the depth direction of the composites layer is observed. Moreover, the transition from the MMC layer to the substrate also exhibits a gradual change in the hardness.

WCp/Ti-6Al-4V graded metal matrix composites layer produced by laser melt injection

WC reinforced surface metal matrix composites (SMMCs) were produced with plasma melt injection (PMI) process on low carbon steel substrate. In the middle and bottom of the SMMC layer, the carbides were mainly M 6 C primary carbides. In the top part, the injected WC particles did not dissolve into the base metal. In the second pass, W content was lower in the top part, and carbides appeared as herringbone structure. In the middle part, M 6 C carbides were larger than those in the single pass. W content was higher in the bottom part, and carbides appeared as WC or partially dissolved tungsten carbides.

Dejian Liu

Papers

WCp/Fe metal matrix composites produced by laser melt injection

Electron microscopy study of reaction layers between single-crystal WC particle and Ti–6Al–4V after laser melt injection

WCp/Ti-6Al-4V graded metal matrix composites layer produced by laser melt injection

WC reinforced surface metal matrix composite produced by plasma melt injection

In situ investigation of fracture behavior in monocrystalline WCp-reinforced Ti–6Al–4V metal matrix composites produced by laser melt injection