Guoliang Hou

Influence of Heat Treatment on Microstructure and Sliding Wear of Thermally Sprayed Fe-Based Metallic Glass Coatings

Fe62Ni3Cr4Mo2W3Si6B17C3 amorphous coatings were thermally sprayed by a high velocity oxygen fuel spraying system (DJ-2700) and heat-treated at the temperatures ranges from 873 to 1,173 K in vacuum for 1 h. Differential scanning calorimetry, X-ray diffraction (XRD), and scanning electron microscopy were used to study the microstructural characteristics of the coatings. Vickers hardness tester was used to measure the hardness of the coatings. At the same time, the sliding wear behavior of the coatings was evaluated in a reciprocating ball-on-disk system. Within the resolution of XRD, amorphous structure without apparent crystalline phases was obtained in the as-sprayed coating. The heat treatments above 873 K led to the crystallization of amorphous phase. With the increase of heat treatment temperature, diffusion and sintering could occur between the layers of the coatings. The highest microhardness was obtained in the coating heat-treated at 973 K. When wear tested at a relative low load of 2 N, a direct correlation between the hardness and wear resistance of the coatings seems to be reasonable. However, at relative high loads, the wear resistance of the coatings is dependent on the resistance to crack initiation and growth between the layers rather than the hardness.

Bioinspired Smart Coating with Superior Tribological Performance

Inspired by the structure of cancellous bone and the nutrition metabolism of articular cartilage, we present a novel concept for a synthetic articular-cartilage-like material. The bioinspired material possesses a low coefficient of friction even under ultrahigh loads and has an extremely long lifetime. Furthermore, the composite shows zero-wear behavior and causes negligible wear damage to the friction pair. The superior tribological performance is attributed to the spontaneously generated articular-cartilage-like layer, which is constantly replenished by frictional heat and pressure. Our findings open a new area for industrial scale engineering applications to improve the friction and wear properties of moving components.

Effect of heat treatment on wear behaviour of WC–(W,Cr)2C–Ni coating

Abstract Tungsten carbide (WC)–(W,Cr)2C–Ni coatings have been deposited by high velocity oxyfuel spraying. The influence of post-vacuum heat treatment on the microstructure, phase composition, microhardness and wear resistance of the coatings has been investigated, which is conducted based on analyses of the microstructure and phase composition evolution of the coatings by scanning electron microscopy and X-ray diffraction, as well as measurement of their microhardness with a microhardness tester and evaluation of their friction and wear behaviour with an oscillating friction and wear tester. Results show that after heat treatment above 600°C, crystallisation of amorphous phases occurs, and some new phases rich of Fe and C are generated in the coatings. Moreover, the microhardness and wear resistance of WC–(W,Cr)2C–Ni coatings increase with increasing heat treatment temperature up to 600 and 700°C, but they tend to decrease with further elevating heat treatment temperature.

Friction and Wear Behavior of Plasma-Sprayed Al2O3-13 wt.%TiO2 Coatings Under the Lubrication of Liquid Paraffin

Two types of ceramic composite coatings (denoted as N-AT13 coating and M-AT13 coating) were fabricated on 1Cr18Ni9Ti stainless steel substrate from ultra-fine and coarse Al2O3-13%TiO2 feedstocks by air plasma spraying. The friction and wear behavior of as-prepared coatings sliding against Al2O3 and stainless steel balls under the lubrication of liquid paraffin was evaluated with an SRV friction and wear tester (Optimol, Germany). The fractured and worn surfaces of the coatings were observed using a scanning electron microscope and a field-emission scanning electron microscope; and the wear mechanisms of the coatings were discussed based on scanning electron microscopic analysis and energy dispersive spectrometric analysis. Results show that N-AT13 coating possesses a unique microstructure and strong inter-splat bonding, thereby showing increased microhardness and bonding strength as well as much better friction-reduction and wear resistance than M-AT13 coating. Moreover, there exist differences in the wear mechanisms of N-AT13 and M-AT13 coatings which slide against ceramic and stainless steel balls under the lubrication of liquid paraffin. Namely, with the increase of normal load, the burnishing of N-AT13 coating coupled with Al2O3 ball is gradually transformed to grain-abrasion and deformation, while M-AT13 coating is dominated by grain-pullout and brittle fracture in the whole range of tested normal load.

Effect of substrate preheating treatment on the microstructure and ultrasonic cavitation erosion behavior of plasma-sprayed YSZ coatings

Inconel 718 was used as the substrate and preheated at different temperatures to deposit yttrium stabilized zirconia (denoted as YSZ) coatings by atmospheric plasma spraying. The microstructure of the as-deposited YSZ coatings and those after cavitation-erosion tests were characterized by field emission scanning electron microscopy, Raman spectroscopy, and their hardness and toughness as well as cavitation-erosion resistance were evaluated in relation to the effect of substrate preheating temperature. Results indicate that the as-deposited YSZ coatings exhibit typical layered structure and consist of columnar crystals. With the increase of the substrate preheating temperature, the compactness and cohesion strength of coatings are obviously enhanced, which result in the increases in the hardness, elastic modulus and toughness as well as cavitation-erosion resistance of the ceramic coatings therewith. Particularly, the YSZ coating deposited at a substrate preheating temperature of 800 °C exhibits the highest hardness and toughness as well as the strongest lamellar interfacial bonding and cavitation-erosion resistance (its cavitation-erosion life is as much as 8 times than that of deposited at room temperature).

A new methodology to prepare ceramic-organic composite coatings with good cavitation erosion resistance

A simple, scalable and economical method was proposed to obtain ceramic-organic composite coating with excellent comprehensive properties include hardness, toughness, elastic recovery, lamellar interfacial bonding and anti-cavitation erosion: introducing epoxy resin into the pores and micro-cracks of plasma sprayed ceramic coating. The results indicate that the epoxy resin was successfully penetrated into the whole ceramic coating and filled almost all defects by vacuum impregnation, which greatly enhanced its compactness and mechanical properties. The bonding strength between top coating and metal interlayer significantly increased from 17.3 MPa to 53.0 MPa, and the hardness (H) of top coating greatly increased from 11.07 GPa to 23.57 GPa. Besides, the value of H3/E2 also increased from 0.06 GPa to 0.15 GPa, meaning the toughness of ceramic coating had been obviously improved. The pure ceramic coating had been punctured only after 4 h of cavitation test. However, the resin with high elasticity and toughness can effectively absorb impact energy, prevent cracks propagation and delay splats spallation during the cavitation erosion process. The novel composite coating displayed far better cavitation erosion resistance than pure ceramic coating, and it was still intact after 10 h of test.

Influence of phase composition on fretting wear behavior of thermally sprayed aluminum bronze coatings

Single α-phase and duplex (α+β′) phase aluminum bronze (CuAl) coatings were deposited on 1Cr18Ni9Ti stainless steels by atmosphere plasma spray. The fretting wear behaviors of the two types of coatings were investigated in relation to their phase composition. The damage mechanisms of the coatings were identified by analysing their worn surfaces using scanning electron microscopy and three-dimensional non-contact surface profiler. A discussion about the identified fretting damage mechanisms was carried out. Results show that duplex CuAl coating has higher hardness than the single α-phase CuAl coating but the former has poorer resistance against fretting wear than the latter in mixed stick-slip regime and gross slip regime. The toughness reduction due to the dendritic distribution of the β′ phase in duplex CuAl coating could explain the low fretting wear resistance observed in the duplex coating. In stick regime, single α-phase CuAl coating has a lower friction coefficient but it has a higher wear rate than the duplex coating, which is attributed to the lower hardness and hence more severe plastic deformation.