The effect of hot isostatic pressing (HIPing)‐induced porosity difference on the fatigue behavior and fracture mechanism of A319 aluminum alloy under uniaxial and nonproportional multiaxial loading is investigated. Non‐HIPed alloy exhibits weaker nonproportional additional hardening capacity than HIPed alloy, which is ascribed to the nonproportional multiaxial loads that enhance the cyclic softening induced by casting pores. Additional plastic damage caused by nonproportional multiaxial loads is highly susceptible to HIPing. Torsional loads trigger the tension‐compression asymmetry of the axial stress response during nonproportional multiaxial fatigue. Multiaxial fatigue life is more sensitive to HIPing at minor total strain amplitudes. The rapid bridging among adjacent pores serves as the preferred channel for fatigue crack propagation. Nonproportional multiaxial loads improve the probability of encountering pores during fatigue crack initiation and propagation.
The A359-SiCp/Fe interpenetrating phase composites reinforced with three-dimensional network structure iron foam and 20 wt. % SiC particles were fabricated after the infiltration technique by using the newly developed vacuum assisted infiltration procedures. The dry-sliding tribological behavior of A359-SiCp/Fe composites was investigated using the HT-1000 ball-on-disc type high temperature tribometer. The samples were subjected to a variety of temperatures and applied loads to investigate the influence on the wear rate and friction coefficient. In this study, SEM was used to analyses the wear microscopic morphology of A359-SiCp/Fe composites reinforced by iron foam. The wear longitudinal section and the morphology of the wear debris were analyzed by EDS and determined to explore the high-temperature wear mechanism under different temperatures and loads. Hardness analysis from the outer periphery to the core revealed an improvement in hardness. The hardness distribution of the wear longitudinal section is different at different temperatures. The formation of a high-hardness mechanical mixed layer with a different thickness on the wear surface can effectively reduce the wear rate. Microstructural investigations demonstrated that the change in wear debris shape with increasing temperature is mostly related to the change in wear mechanism. Abrasive wear and oxidation wear are the main wear mechanisms. With an increase in temperature and plastic deformation, delamination and adhesion are the predominant wear mechanisms, accompanied by the additional oxidative wear.
Purpose
To improve the high-temperature wear properties of the SiCp/A359 composite, foamed iron-reinforced SiCp/A359 composite (A359–SiCp/Fe) is prepared. The purpose of this study is to investigate the tribological behavior and mechanism of the A359–SiCp/Fe composites at different temperatures (100–500 °C) and loads (7 N, 10 N and 12 N).
Design/methodology/approach
The A359–SiCp/Fe composite was fabricated by vacuum-assisted infiltration. The dry sliding tribological behaviors of A359–SiCp/Fe composite were investigated using the ball-on-disc-type tribometer. The worn surface and wear morphology of the longitudinal section were examined using field emission scanning electron microscopy and metallographic microscope.
Findings
The critical transition temperature for severe wear in A359–SiCp/Fe composite was 50–100 °C higher than in SiCp/A359 composite. Foamed iron prevents exfoliation cracks from penetrating deeper into the matrix. The friction coefficient stability of the A359–SiCp/Fe composite was higher than the unreinforced composite at elevated temperatures. With the increase in temperature, the friction-affected layer was severely worn, and the wear mechanism transferred from abrasion and delamination to oxidation and plastic flow, respectively.
Originality/value
The preparation procedure for aluminum matrix composites reinforced with foamed metal has been less reported, and the research on the tribological behavior and mechanism of A359–SiCp/Fe composite at various temperatures is insufficient. The foamed iron structure considerably enhances the wear properties of SiCp/A359 composite in elevated temperature conditions.
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