Xiaowen Qi

Wear resistance of hypereutectic Fe-Cr-C hardfacing coatings with in situ formed TiC

Abstract With excellent wear resistance, hypereutectic Fe–Cr–C coatings have caused great attention in the field of surface engineering. In this study, the hypereutectic Fe–Cr–C hardfacing coatings with certain amounts of titanium (Ti) additives were further developed. The precipitation of the carbides in the coatings was calculated. The microstructure of the coatings was observed and the phase structure of the coatings was determined. Besides, the wear resistance of the coatings was also measured. The experimental results show that the microstructure of the coatings mainly consists of primary (Cr,Fe)7C3 carbide and eutectic matrix. With increasing Ti additive, the primary carbide is refined, which in turn improves the wear resistance of the coatings.

Self-Repairing Characteristics of Serpentine Mineral Powder as an Additive on Steel–Chromium Plating Pair under High Temperature

Friction and wear experiments on steel–chromium plating pairs were carried out with nanoscale serpentine (a magnesium silicate mineral) as a lubricating oil additive at 400°C. The tribological test results showed that self-repairing protective layers formed on the contact surfaces of both the steel matrix and hard chromium coating. Field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS) analysis demonstrated that the morphology and elements of self-repairing layers were in accordance with that of serpentine. A generation mechanism of the layer was proposed that suggests that isomorphic replacement between Fe/Cr and serpentine mineral silicate occurs, which is the wear mechanism of the tribochemical reaction.

Effects of Kevlar® 29 yarn twist on tensile and tribological properties of self-lubricating fabric liner

Yarn twist in textile technology is an important characteristic since it considerably affects the properties of knitted or woven fabrics. Many researchers have investigated the effect of staple-spun yarn twist on the properties of the yarns and fabrics. However, the effects of twist level of Kevlar® 29 filament yarn on the properties of yarn and its resin-impregnated self-lubricating fabric liner are not fully known yet. In this study, we have investigated the effects of Kevlar® 29 twist level on the tensile and tribological properties of the fabric liner (Kevlar® 29/polytetrafluoroethylene fabric-resin composite). Two unexpected findings about the effect of yarn twist have been observed, namely (1) asynchronous twist effect on the yarn’s and the liner’s tensile strength and (2) dissimilar yarn twist effect on the liner’s performance. These findings are mainly attributed to the synergic contributions of the yarn twist and strength and the interaction of the resin with the yarn orientation in the woven fabric structure of the liner.

Influence of 3-aminopropyltriethoxysilane- graphite oxide composite on thermal stability and mechanical property of polyethersulfone

Graphite oxide (GO) was modified using 3-aminopropyltriethoxysilane (APTES) for the fabrication of sheet type APTES–GO composite. Then, this composite was incorporated into the polyethersulfone (PES) matrix to enhance the thermal and mechanical properties of this polymer. The influence of APTES–GO composite on the thermal stability and mechanical property of PES was evaluated. The surface modification of GO by interacting with APTES could be an effective method to improve the compatibility and dispersion of GO sheets within the PES matrix. In comparison with those of virgin PES and GO/PES composites, the thermal decomposition temperature of PES composites containing well-dispersed APTES–GO sheets increased by 18.7°C. The tensile strength, tensile modulus, flexural strength, and flexural modulus of PES composite reinforced with 1.0 wt% APTES–GO sheets were enhanced by 21.1%, 15.2%, 15.4%, and 12.8%, respectively. The enhancement in thermal stability and mechanical property of APTES–GO/PES composite can be attributed to the uniform dispersion of APTES–GO sheets in the PES matrix as well as the strong interfacial interaction between them.

Fatigue failure of 45# steel in dry sliding against Kevlar/PTFE hybrid composite under elevated load

Frictional failure is inevitable for friction pairs. A common sense about the frictional failure of steel-polymer composite friction pair is that the polymer composites are the primary failure part rather than the steel counterpart. However, an opposite case was newly found in the case of fabric self-lubricating liner (Kevlar/PTFE hybrid composite) spherical plain-bearing under elevated load: the steel counterbody suffered a fatigue failure before the fabric composite fails, which resulted in the final failure of the bearing. This paper investigated such fatigue failure of surface chrome plated 45# steel by systematically studying the wear characteristics of 45# steel and fabric composite, the stress distribution of the 45# steel and fatigue features within cross section of the 45# steel. Results showed that wear characteristics of both fabric composite and 45# steel exhibited regional characters. Failure mechanism of the 45# steel was found to be fatigue failure (mainly fatigue pitting), which was revealed by mathematical analysis of the stress distribution of the 45# steel and the fatigue cracks found within subsurface of the cross section of the 45# steel.