Weihao Xiong

Microstructure and cutting performance of Ti(C, N)-based cermets heat-treated in nitrogen

Abstract Ti(C, N)-based cermets were treated using hot isostatic pressing (HIP) at 1423 K in nitrogen. The microstructures compared with the as-sintered cermets were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray analysis, and electron microprobe analysis. It was found that high nitrogen activity in the surface zone resulted in the formation of gradient structure. Approximately 20-μm-deep, nitrogen-rich and titanium-rich hard surface zone was introduced by the heat treatment. The nitrogen activity was the driving force that caused the transportation of the atoms through the binder, titanium towards the surface, and tungsten and molybdenum inwards. In the surface zone, the particle size became fine, the inner rim disappeared, and the volume fraction of the outer rim and the binder phase considerably reduced. Small grains of TiN, WC, Mo 2 C, and nitrogen-rich carbonitride phases formed in the surface zone during the heat treatment, improving the tribological property of the heat-treated cermet.

Effects of adherends recycling on the distribution of hardness in bonded region of adhesively bonded single lap joints

The phenomenon of work hardening in the bonded region of steel adherends has been studied, and the effect of adherends recycling on the shear strength of a single lap joint is analyzed in this paper. The values of hardness on the surfaces of failed joints were measured after being simply treated (removing the adhesive layer by solvent) before the specimen preparation next time. Mild steel or pure copper sheet and an epoxy adhesive were used to prepare the single lap joints and the same couple of adherend pieces underwent three or four times of strength and hardness tests. The results obtained show that the evident hardness change occurred after the adherends passed their first or second strength testing and most of the points tended to increase their values of hardness as the tests were performed. It may be due to the contribution of the stress concentration during loading, and the residual stress occurred after the adherends unloading. The results obtained also show that the increase of hardness occurring in the bonded zone is greater than that on the face opposite to the bonded region. The distribution of micro-hardness was verified by the strain gauges testing method.

Effect of warm compaction and microwave sintering on the densification, tribological and electrochemical properties of TiC/316L composites

Abstract In this study, TiC/316L stainless steel composites were fabricated by combining warm compaction and microwave sintering (WMS). X-ray diffraction analysis was used to identify the phases in the material. Microstructure characteristics of composites were performed by means of scanning electron microscopy (SEM). Density, microhardness, wear resistance, and corrosion resistance were evaluated at room temperature. Results revealed that TiC/316L composites with higher relative density and finer properties can be obtained by WMS, compared with conventional powder metallurgy process. For all the tested species, the hardness of the composites prepared by WMS is higher than that of the composites prepared by conventional powder metallurgy (P/M). Wear tests showed that the WMS species exhibited significantly good wear resistance. Furthermore, it is found that the composites prepared by WMS were not only has high mechanical properties but also better corrosion resistance compared with the conventional P/M species.

Effect of Vacuum-Sintering Temperature on Magnetic and Mechanical Properties of TiC-TiN-Ni-Mo-C Cermets

The effect of vacuum-sintering temperature (Tvs), ranging from 1390 °C to 1470 °C, on magnetic and mechanical properties of TiC-10TiN-30Ni-6Mo-4C (mol pct) cermet was investigated in the present article. Room-temperature (RT) magnetization and maximum susceptibility decreased with increasing Tvs up to 1450 °C, and then increased. This was mainly attributed to the fact that Ti content in the Ni-based binder phase increased with increasing Tvs up to 1450 °C, suppressing ferromagnetism of the Ni matrix. RT ferromagnetism disappeared at Tvs ≥ 1430 °C. Transverse rupture strength (TRS) reached a peak value at Tvs = 1430 °C, and hardness did not significantly vary with Tvs.