Purpose
This study aims to investigate the effects of graphite-MoS2 composite solid lubricant on the tribological properties of copper-based bearing materials under dry conditions.
Design/methodology/approach
The mixture of Graphite-MoS2 was inlaid in ZQSn6-6–3 tin bronze and ZQAl9-4 aluminum bronze matrix. These copper-embedded self-lubricating bearing materials were considered in friction pairs with 2Cr13 stainless steel, and their tribological properties were studied by using an MM200 wear test machine.
Findings
The results show that the friction coefficients and wear rates of copper-embedded self-lubricating bearing materials are lower than those of the ordinary copper-based bearing materials. The wear performance of the tin bronze inlaid self-lubricating bearing material is better than that of the aluminum bronze inlaid self-lubricating bearing material. The wear mechanism of the tin bronze bearing material is mainly adhesive wear, and that of the aluminum bronze bearing material is mainly grinding wear, oxidation wear and adhesive wear. The copper-embedded self-lubricating bearing materials had no obvious abrasion, whereas the aluminum bronze inlaid self-lubricating bearing material exhibited deep furrows and obvious abrasion under high loads.
Originality/value
These results are helpful for the application of copper-embedded self-lubricating bearing materials.
In this paper, the abnormal fracture failure of a ZL104 aluminum alloy quick-opening manhole cover of a cement tank truck is systematically studied to discover the root cause of an accident. The unloading operation procedures of cement tank trucks, the effectiveness of safety valves, the chemical composition, mechanical properties and material quality of aluminum alloy manhole covers, and the macroscopic and microscopic morphology of fractures were comprehensively analyzed. The results show that although the Mg content in the chemical composition of an aluminum alloy manhole cover exceeds the standard, it is not the root cause of the accident. The root cause of the failure is that, during the unloading operation, the operator did not strictly follow the unloading procedures. One of the buckles was in the released state, which led to uplift cracking, resulting in the successive cracking and slipping of adjacent buckles, and the manhole cover finally cracked and flew out. Based on the failure causes, suggestions are put forward to prevent the manhole cover from failing during the unloading operation of cement tank trucks in the future.
The study of the deformation and fracture mechanisms of power plant materials at elevated service temperature is of utmost importance in structural integrity assessment. In this work, interrupted miniature uniaxial tensile tests (MUTT) have been conducted to investigate the fracture evolution mechanisms for a Grade 91 steel at 600°C. The engineering stress–strain curves of the MUTT can be divided into six different stages, including the elastic stage, strain hardening stage, homogeneous plastic deformation stage, necking across the transverse and thickness direction stage, and finally, the fracture propagation stage. In addition to full history tests, MUTT were interrupted in each of the different stages to study the entire failure process evolution from the uniform deformation, necking to specimen separation, using optical microscopy and Scanning Electron Microscope (SEM). It has been shown that the necking of the interrupted testing specimens appears at Stage IV across the width direction prior to the thickness direction at Stage V. The thickness direction necking would lead to fracture rapidly. The void coalescence directly caused by damage has been observed in Stage VI.
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