Wear behavior of laser metal deposited 17-4 PH SS-W composite at varied tungsten powder flow rate

This research studies the wear behavior of laser metal deposition of 17-4 PH SS-W composite using a 6 mm alumina-stainless steel ball under a load of 10 N, for 16 minutes, 40 seconds and with acquisition rate of 100 Hz conducted at 25 °C. The effect of laser power of between 2600 W and 1500 W; and powder flow rate of between 0.5 min⁻¹ and 2.0 min⁻¹ on wear resistance is investigated. Other processing parameters are constant throughout the experiments. The results show that the 17-4 PH SS-W composite produced at a high laser power of 2600 W exhibits a higher wear resistance as compared to the 17-4 PH SS-W composite samples produced at low laser power of 1500 W. The 17-4 PH SS-W composite sample produced at high laser power of 2600 W with tungsten powder flow rate of 2.0 min⁻¹ has the highest wear resistance with wear volume of 0.0276 mm³ and wear rate of 8.8 ⋅ 10⁻⁵ mm³/N m while the 17-4 PH SS-W composite sample produced at a low laser power of 1500 W with tungsten powder flow rate of 1.0 min⁻¹ has the wear volume of 0.02834 mm³ and wear rate of 9.0 ⋅ 10⁻⁵ mm³/N m.     

Influence of size and volume share of WC particles on the properties of sintered metal matrix composites

Steel matrix composites are being increasingly investigated because of their wear and corrosion properties, allowing their wide application in various industrial sectors. The interaction of tungsten carbide (WC) with the steel matrix, including an analysis of its volume share and particle size, is crucial in determining the resistance to wear and corrosion of the metal matrix composite (MMC). However, there is little information in the literature about sintered MMCs based on low-alloy steels. This paper presents the results of an analysis of the influence of the volume share of WC (5?vol.% and 20?vol.%) and carbide particle size (0.7?µm and 5.0?µm) on the resistance to abrasion of a friction pair: sintered composite and bearing steel, analysed using two rotational speeds (0.02?m/s and 0.2?m/s). Moreover, the resistance to corrosion in 3.5% NaCl solution is also characterized. It is shown that both the volume share and the size of the WC particles used as reinforcement of the steel matrix have a significant impact on the densification behaviour as well as the resistance to abrasive wear and corrosion of sintered MMCs based on low-alloy steel.     

Formation mechanisms of low-friction tribo-layers on arc-evaporated TiC1−xNx hard coatings

A detailed correlation of the tribological performance of arc-evaporated TiC_1−xN_x coatings with testing temperature, atmosphere as well as variation in load and sliding velocity is presented in this paper. The low-friction behavior in combination with its mechanical integrity are the reasons for the extensive industrial application of TiC_1−xN_x over the last decades. Still the tribo-mechanisms behind this performance are not yet completely understood. The present study adds further understanding, as the low-friction behavior degrades at elevated temperatures and dry or inert environments, which is related to the different constitution of the tribo-layer formed as investigated by Raman spectroscopy. Surprisingly, the wear rate of the coatings does not correlate with the coefficient of friction indicating the presence of different wear regimes.     

Effect of quartzite and granite in wear surfaces on dry sliding

Abstract

The wear surfaces abraded with quartzite and granite were subjected to scratch tests. Sharp and blunt indenters were used with various constant loads to produce controlled abrasive wear tracks. The characteristics of deformation mechanisms and material removal were further studied using a scanning electron microscope to determine the differences in the tribological behaviour between the quartzite and granite wear surfaces.

The results indicate that quartzite residues are more uniformly distributed as individual particles on the wear surfaces and therefore provide more stable frictional forces. In the case of granite the abrasive residues are rather non-uniformly collected into piles of abrasives.     

Modelling of plowing and shear friction coefficients during high-temperature ball-on-disc tests

During high-temperature ball-on-disc tests of aluminium against steel, hot aluminium deforms and wear track evolves. The individual contributions of plowing and shearing to the apparent friction and the contact pressure are unknown. The aim of the research was to develop a model capable of determining these parameters. It was found that during high-temperature ball-on-disc tests, the plowing friction accounted for only about 1% of the apparent friction, although the plowing friction coefficient increased with increasing wear lap, while the shear friction played a dominant role in determining the apparent friction measured. The mean contact pressure decreased significantly as the test proceeded.     

基于虚拟仪器技术的小型球盘式摩擦磨损试验机的研制

为了初步检测各种涂层试样的摩擦磨损特性,设计一台小型球盘式摩擦磨损试验机。该试验机结构简单,测试系统软件在虚拟仪器技术基础上采用LabVIEW平台开发,实现了对数据的实时采集、处理和结果显示。试验证明,该试验机能满足涂层试样摩擦磨损试验研究需要。     

Effect of temperature on the frictional behaviour of an aluminium alloy sliding against steel during ball-on-disc tests

Ball-on-disc tests were carried out at elevated temperatures to determine the friction behaviour of the 7475 aluminium alloy against steel, resembling the material mating during hot extrusion. Friction coefficient was found to increase markedly with rising temperature, suggesting that the commonly accepted assumption of an unvaried friction coefficient in the FE simulation of the aluminium extrusion process involving temperature evolution is incorrect. A theoretical analysis showed that the high friction values measured during high-temperature ball-on-disc tests could be partly attributed to the increased plowing friction caused by the severe deformation of the aluminium alloy. The effect of temperature on the stress and strain distributions at the ball/disc interface was revealed by means of three-dimensional finite-element (3D FE) simulation. Increased deformation in the aluminium disc around the contact point with rising temperature was confirmed. The alterations of the strain state and stress state around the contact point were considered responsible for the generation of wear debris, the oscillations of friction coefficient along the wear track and the increase of friction coefficient with rising temperature.     

Wear maps of HIP sintered Si3N4/MLG nanocomposites for unlike paired tribosystems under ball-on-disc dry sliding conditions

Hot isostatically pressed monolithic and multilayer graphene (MLG) reinforced silicon nitride nanocomposites have been investigated by ball-on-disc tests under variable loading conditions. Tests were carried out at room temperature with three different normal loads (10, 40 and 80 N), and six sliding speeds (10, 20, 50, 100, 150 and 200 mm/s) without lubrication using commercial silicon carbide ball counterparts for 54 tribosystems. The aim of the research work was to construct 2D wear transition and 3D wear rate maps of the investigated ceramic composites. The 3D maps visualizing the specific wear rate and the dimensionless wear coefficient as a function of normal load and sliding speed have been completed with morphological analysis of wear tracks and identification of the dominant wear mechanisms. The presented ceramic wear maps provide useful aid for predicting the wear performance of the investigated nanocomposites under various loading conditions.     

On dry sliding friction and wear behaviour of PEEK and PEEK/SiC-composite coatings

In this work, polyetheretherketone (PEEK) and PEEK/SiC-composite coatings were deposited on Al substrates using a printing technique to improve their surfaces performance. The objective of this work was to investigate coatings friction and wear behaviour. Especially, the effect of sliding velocity and applied load on coatings friction coefficient and wear rate was evaluated in range of 0.2-1.4 m/s and 1-9 N, respectively. Compared to Al substrate, the coated samples exhibit excellent friction coefficient and wear rate. For PEEK coating, under an applied load of 1 N, the increase in sliding velocity can result in decreasing of friction coefficient at a cost of wear resistance. Under a load of 9 N, however, PEEK coating exhibits the highest friction coefficient and wear rate at an intermediate velocity. These influences appear to be mainly ascribed to the influence of contact temperature of the two relative sliding parts. In most test conditions, the composite coating exhibits better wear resistance and a little higher friction coefficient. SiC reinforcement in composite coating plays a combined role. First of all, it might lead to energy dissipation for activation of fracture occurred on the interface of PEEK and the powders. Moreover, it can reduce coating ploughs and the adhesion between the two relative sliding parts.     

Tribological mechanism and property of 9Cr18 friction pair at atmosphere and in vacuum

In this paper, the comparative tribological property of 9Cr18 friction pair used for aerospace components was investigated using a ball-on-disc tester in four different service conditions: in air, in vacuum, and with or without MoS₂-based film. The results indicate that the friction coefficients of the 9Cr18 couplings with MoS₂ solid lubrication or in vacuum are much lower than those in the conditions of dry friction or atmosphere, with relatively flat ground trace surfaces. While the friction coefficients of usual materials of friction pairs in vacuum are higher than those in atmosphere, it is shown in our study that the abnormal performance may be induced by the surface hardenability of dry friction transition and the lubrication effect of the MoS₂-based film. At the same time, the tribological mechanism of the pair is considered as well.