On the Grinding Performance of Alumina Wheels in Ultrasonic Vibration-Assisted Grinding of Hardened GCr15 Steel

Composite manufacturing with multiple energy fields is an important source of processing technology innovation. In this work, comparative experiments on the conventional grinding (CG) and ultrasonic vibration-assisted grinding (UVAG) of hardened GCr15 steel were conducted with WA wheel. The grinding wheel wear patterns and chips were characterized. In addition, grinding force, force ratio, and ground surface quality were investigated to evaluate wheel performance. Results illustrate that the interaction between abrasive grains and workpiece in UVAG process has the characteristics of high frequency and discontinuity. The wear property of abrasive grains is changed and the grinding force is decreased because the generation of micro-fracture in abrasive grains improves the grinding wheel self-sharpening. Better surface quality is obtained, the surface roughness is reduced by up to 18.96%, and the number of defects on the machined surface is reduced through the superior reciprocating ironing of UVAG. Accordingly, WA wheel performance is improved by UVAG.

Comparison on the Tribological Properties of Roller and Guide Tribo-Pair Used in Antenna Deployable Structure

The tribological properties of roller and guide tribo-pair are important for the design of deployable structure for space-borne perimeter truss antenna. In this study, carbon fiber epoxy resin composites are used as the guide material; while polyimide and GCr15 steel are used as the roller material. Then, friction coefficient of polyimide ball and GCr15 steel ball against carbon fiber epoxy resin composites disk were compared and investigated on the high-temperature, ball-on-disk tribometer under different operating conditions, respectively. The wear morphology of disk was measured by laser scanning confocal microscope. The results show that the friction coefficient of the polyimide ball against carbon fiber epoxy resin composites tribo-pair has better tribological properties. Meanwhile, the friction coefficients of this pair are mainly depend on abrasive wear under low pressure and velocity conditions while the adhesive wear has dominated influence on the friction coefficient for high pressure and velocity conditions. Besides, the tribological properties of carbon fiber epoxy resin composites are mainly affected by ploughing of surface roughness at low temperature, while by surface debonding at high temperature.

Numerical Simulation of Microstructure Evolution during Continuous Hot Rolling Process of GCr15 Steel Rod

In this paper, the microstructure evolution during continuous hot rolling process of GCr15 steel rod was investigated. A series of multi-field coupled finite element models were established based on commercial finite element software MSC.Marc. The kinetics equations of austenite grain size evolution of GCr15 steel were coupled to these models by a designed MSC.Marc subprogram. The field variables, including temperature, equivalent stress, equivalent strain, and equivalent strain rate, were calculated. The distributions of dynamic recrystallization, metadynamic recrystallization, and static recrystallization fractions were investigated. The distribution and evolution of austenite grain size at different stages in the continuous hot rolling process were analyzed. To verify the models, the temperatures of GCr15 steel rod at different stages in the continuous hot rolling process were measured. And the austenite grain sizes at cross section of the rod after the continuous hot rolling process were measured. The simulation results show a good agreement with the experimental results.

Exploring the role of −NH2 functional groups of ethylenediamine in chemical mechanical polishing of GCr15 bearing steel

Ethylenediamine with two −NH2 functional groups was used as a critical complexing agent in chemical mechanical polishing (CMP) slurries for a high carbon chromium GCr15 bearing steel (equivalent to AISI 52100). The polishing performance and corresponding mechanism of −NH2 functional groups were thoroughly investigated as a function of pH. It is revealed that, when polished with ethylenediamine and H2O2-based slurries, the material removal rate (MRR) and surface roughness Ra of GCr15 steel gradually decrease as pH increases. Compared with acidic pH of 4.0, at alkaline pH of 10.0, the surface film of GCr15 steel has much higher corrosion resistance and wear resistance, and thus the material removal caused by the pure corrosion and corrosion-enhanced wear are greatly inhibited, resulting in much lower MRR and Ra. Moreover, it is confirmed that a more protective composite film, consisting of more Fe3+ hydroxides/oxyhydroxides and complex compounds with −NH2 functional groups of ethylenediamine, can be formed at pH of 10.0. Additionally, the polishing performance of pure iron and a medium carbon 45 steel exhibits a similar trend as GCr15 steel. The findings suggest that acidic pH could be feasible for amine groups-based complexing agents to achieve efficient CMP of iron-based metals.

Tribological Performance of Steel With Multi-Layer Graphene Grown by Low-Pressure Chemical Vapor Deposition

To explore the potential of directly grown multi-layer graphene as an agent in reducing friction and wear of steel on steel tribo-pair, multi-layer graphene films were synthesized on GCr15 steel in a low-pressure chemical vapor deposition (LPCVD) setup using a gaseous mixture of acetylene and hydrogen onto a bearing steel substrate. An interlayer of electroplated nickel was deposited on steel to assist and accelerate the graphene deposition. The tribological performance was evaluated using a ball-on-disc tribometer with an average Hertzian pressure of 0.2, 0.28, 0.34, and 0.42 GPa over a stroke length of 5 mm against GCr15 steel ball and compared with bare steel and nickel-plated steel. The results indicate that the friction coefficient is dependent on the applied load and decrease with increasing load, and the minimum friction coefficient of ∼0.13 was obtained for an applied normal load of 1 N; however, the coating failed after 250 cycles. The decrease in friction coefficient has been attributed to the homogenization of the deposited multi-layer graphene along the sliding direction and transfer of graphene to counter-face ball leading to inhibition of metal-metal contact. The investigation suggests that this kind of coating has the potential of improving the tribological performance of metal-metal tribo-pairs.