Hanshan Dong

Enhanced wear resistance of titanium surfaces by a new thermal oxidation treatment

Abstract The wear behaviour of thermal oxidation (TO)-treated as well as untreated Ti6Al4V alloy has been investigated using an Amsler tribometer in rolling–sliding motion under boundary lubrication conditions. The results show that the TO treatment can significantly enhance the wear resistance of Ti6Al4V alloy. Based on the experimental results, in conjunction with systematic analyses, the wear-reduction mechanisms involved in the TO-treated material are discussed. It was found that the significantly reduced tendency to adhesive wear and the improved wettability, which increases the effectiveness of lubrication, have contributed to the enhanced wear resistance of the TO-treated material.

Realising the potential of duplex surface engineering

Abstract We are now close to the new millennium and on the threshold of an era of rapid change. Limitations to the further advance of manufacturing industry in the 21st century are most likely to be surface-related. Many mechanical systems will operate under ever more severe application conditions, such as intensive loads, high speeds and harsh environments, in order to achieve high productivity, high power efficiency and low energy consumption. Consequently, many challenging complex design situations have emerged where the combination of several properties (such as wear resistance, load bearing capacity, and fatigue performance) are required. These new challenges can be met only through realising the potential of duplex surface engineering. Indeed, there are thought to be great technical and economic benefits available through the application of duplex surface engineering technologies in many new market sectors. The present paper is a synthesis of several strands of recent surface engineering research at the University of Birmingham, including the duplex ceramic coating-nitrided steel system and the duplex DLC coating–oxygen diffusion treated titanium system. The prediction of the performance of duplex systems based on advanced contact mechanics modelling is also discussed.

Oxygen boost diffusion for the deep-case hardening of titanium alloys

In order to withstand the high stresses encountered in such general engineering components as bearings and gears, deep case hardening is necessary. In the present investigation, oxygen boost diffusion of titanium alloys has been explored and a new oxygen boost diffusion technique has been developed for deep case hardening of titanium and its alloys. The oxygen boost diffusion process essentially consists of thermal oxidation in air followed by diffusion in vacuum. A total hardened case of about 300 μm can be successfully achieved following the oxygen boost diffusion treatment. It has also showed that the oxygen boost diffusion treated titanium alloys exhibited significantly improved abrasive wear resistance. Based on the experimental results, the boost diffusion and hardening mechanisms are discussed.

Enhanced corrosion resistance of duplex coatings

Abstract A series of electrochemical tests have been carried out to investigate the corrosion behaviour of physically vapour deposited TiN, CrN and (TiAl)N coatings on plasma nitrided En40B steel. Surface and subsurface characterisation before and after corrosion testing were performed using scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). The experimental results indicate that all three duplex coating systems possess superior corrosion resistance over the individually plasma nitrided or PVD coated En40B steel, highlighting the importance of the iron nitride subsurface in determining the corrosion resistance of duplex coating systems. It is also demonstrated that among these three duplex coating systems, the corrosion resistance increases in the order of TiN/PN, CrN/PN and (TiAl)N/PN. The critical potentials corresponding to the onset of transpassive behaviour for both the CrN/PN and the (TiAl)N/PN duplex coating systems are above the practical potential range (

Improved wear resistance of ultra-high molecular weight polyethylene by plasma immersion ion implantation

Surface modification of ultra-high molecular weight polyethylene (UHMWPE) has been explored using the novel non-line-of-slight plasma immersion ion implantation (PIII) with nitrogen. The modified surfaces were characterised by SEM and a Nano Test 600 testing machine. The tribological behaviour of PIII treated UHMWPE sliding against AISI 316L stainless steel counterfaces was evaluated using a pin-on-disc tribometer under water lubricated conditions. The experimental results show that PIII is a very promising surface engineering technique to improve such surface mechanical properties as surface hardness and elastic modulus of UHMWPE. As a result, the wear resistance of UHMWPE was significantly enhanced by a factor of three following PIII treatment, as compared with untreated material. It was found that the significantly improved wear resistance of PIII treated UHMWPE can be mainly attributed to ion bombardment induced cross-linking, and thus surface hardening.

Tribological behaviour and microscopic wear mechanisms of UHMWPE sliding against thermal oxidation-treated Ti6Al4V

Tribological behaviour of ultra-high molecular weight polyethylene (UHMWPE) pins sliding against thermal oxidation (TO)-treated Ti6Al4V alloy discs with different levels of average surface roughness was investigated under water lubrication conditions. When rubbing against a smooth counterface (RaB 0.030‐0.035 mm), UHMWPE was found to be worn predominantly via a micro-fatigue mechanism. To advance the scientific understanding of the microscopic wear mechanisms of UHMWPE, a technique involving permanganic etching coupled with high resolution SEM analyses of wear surfaces and cross-sections was adopted to yield new insight into the micro-fatigue mechanism. It was found that stress-induced preferential orientation of the crystalline lamellae in the UHMWPE led to the origin of ripples containing micro-cracks at their valleys. The cyclic loading promoted lateral propagation and inter-connection of these micro-cracks, thus giving rise to eventual spallation of the surface material as wear debris. Based on the experimental results, a micro-fatigue wear mode is proposed.

Tribological behaviour of alumina sliding against Ti6Al4V in unlubricated contact

Abstract Tribological behaviour of alumina balls (99.5%) sliding against a Ti6Al4V disc over a range of loads (5–80 N) and speeds (0.0625–1 m s −1 ) has been investigated using a pin-on-disc tribometer under unlubricated conditions. The maximum wear coefficient was observed to be several orders of magnitude higher than the reported value for alumina against alumina or alumina against steel counterfaces. When the load or speed increased, the wear rate of the alumina ball increased initially and then decreased, showing typical transition features. On the other hand, the friction coefficients for the Ti6Al4V/alumina tribosystem were found to increase inversely with the applied loads or the sliding speeds. The wear mechanisms and the wear transition were investigated based on examinations of worn surfaces as well as debris using SEM, XRD and XPS, and it was revealed that a tribochemical mechanism accounted for the observed high wear rate of alumina sliding against the titanium alloy.

Surface engineering of light alloys

Part 1 Surface degradation of light alloys: Corrosion behaviour of magnesium alloys and protection techniques Wear properties of aluminium-based alloys Tribological properties of titanium alloys. Part 2 Surface engineering technologies for light alloys: Anodising of light alloys Plasma electrolytic oxidation treatment of aluminium and titanium alloys Plasma electrolytic oxidation treatments of magnesium alloys Thermal spraying of light alloys Cold spraying of light alloys Physical vapour deposition of magnesium alloys Plasma assisted surface treatment of aluminium alloys to combat wear Plasma immersion ion implantation (PIII) of light alloys Laser surface modification of titanium alloys Laser surface modification of aluminium and magnesium alloys Ceramic conversion treatment of titanium-based materials Duplex surface treatments of light alloys. Part 3 Applications for surface engineered light alloys: Surface engineered light alloys for sports equipment Surface engineered titanium alloys for biomedical devices Plasma electrolytic oxidation and anodised aluminium alloys for spacecraft applications.

Friction-induced nanofabrication on monocrystalline silicon

Fabrication of nanostructures has become a major concern as the scaling of device dimensions continues. In this paper, a friction-induced nanofabrication method is proposed to fabricate protrusive nanostructures on silicon. Without applying any voltage, the nanofabrication is completed by sliding an AFM diamond tip on a sample surface under a given normal load. Nanostructured patterns, such as linear nanostructures, nanodots or nanowords, can be fabricated on the target surface. The height of these nanostructures increases rapidly at first and then levels off with the increasing normal load or number of scratching cycles. TEM analyses suggest that the friction-induced hillock is composed of silicon oxide, amorphous silicon and deformed silicon structures. Compared to the tribochemical reaction, the amorphization and crystal defects induced by the mechanical interaction may have played a dominating role in the formation of the hillocks. Similar to other proximal probe methods, the proposed method enables fabrication at specified locations and facilitates measuring the dimensions of nanostructures with high precision. It is highlighted that the fabrication can also be realized on electrical insulators or oxide surfaces, such as quartz and glass. Therefore, the friction-induced method points out a new route in fabricating nanostructures on demand.

Towards a deeper understanding of the formation of friction-induced hillocks on monocrystalline silicon

Friction-induced hillocks can be produced on monocrystalline silicon by scratching under given conditions. Results show that the height of these hillocks increases with the applied normal load or number of scratching cycles, but decreases with the sliding velocity. Transmission electron microscope (TEM) and energy dispersive x-ray (EDX) analysis show that the hillock contains a thin superficial oxidation layer and a thick disturbed (amorphous and deformed) layer in the subsurface. Although the formation of the silicon hillock is the combined results of mechanical interaction and tribochemical reaction, the mechanical interaction plays a more dominant role. Further analysis indicates that the formation of hillock is mostly induced by the amorphization of crystal silicon during scratching. Low sliding speed is found to facilitate the formation of a thick amorphization layer under the same loading condition. Since the friction-induced hillock is the initial surface damage on the nanoscale, the results will shed new light on understanding and controlling the nanowear process of silicon in micro/nanoelectromechanical systems.