Effect of defect length on rolling contact fatigue crack propagation in high strength steel

The objective of the present paper is to clarify the effect of defect length in depth direction on rolling contact fatigue (RCF) crack propagation in high strength steel. RCF test and synchrotron radiation micro computed tomography (SR micro CT) imaging were conducted. In the case of the defect with the 15 ?m diameter, flaking life decreased with increasing defect length. In a comparison of the CT image and the SEM view, the shapes of defects and the locations of the horizontal cracks were almost the same respectively. The mechanism of RCF crack propagation was discussed by finite element (FE) analysis. Defects led to higher tensile residual stress than that without defects in the region where the defect exists. The shear stress range at 0.1 mm in depth on the middle line of the defect and the range of mode II stress intensity factor at the bottom of a vertical crack increased with increasing defect length.&nbsp

Achieving superplasticity in a Cu-40% Zn alloy through severe plastic deformation

The Cu–40%Zn alloy is a classic two-phase material exhibiting superplasticity at elevated temperatures. This report demonstrates that the application of severe plastic deformation at a temperature associated with a phase transformation leads to grain refinement in the alloy and the development of a superplastic ductility at a high strain rate and relatively low temperature

Grain refinement of copper based alloys Using ECAP

Equal-channel angular pressing (ECAP) was conducted to achieve grain refinement in a series of Cu-based alloys having either a single-phase or a two-phase condition. The phase condition of the alloys was controlled through the introduction of Zn as an alloying element and Zr was also added to provide some thermal stability of the ultrafine-grained structures. Microstructures were observed by optical microscopy and transmission electron microscopy and the tensile properties of the as-pressed alloys were examined at elevated temperatures. It is shown that superplastcity is attained under optimum conditions in both the single-phase and the two-phase alloys after processing by ECAP

Equal-channel angular pressing as a production tool for superplastic materials

Equal-channel angular pressing (ECAP) was applied for grain refinement of Al-3%Mg0.2%Fe and Al-3%Mg-0.2%Ti alloys and also for a commercial Al 2024 alloy. The grain sizes of the alloys were reduced to similar to0.3 mum. The stability of the fine-grained structures were examined and it was found that the small grains remained stable up to the temperatures of similar to 250 degreesC for the Al-3%Mg-0.2%Fe and Al-3%Mg-0.2%Ti alloys and similar to 400 degreesC for the Al 2024 alloy. Tensile tests revealed maximum elongations of similar to 370% and similar to 180% in the Al-3%Mg0.2%Fe and Al-3%Mg-0.2%Ti alloys, respectively, at a temperature of 250 degreesC with an initial strain rate of 3.3x10(-4) s(-1). There is some evidence for low temperature superplasticity in the Al-3%Mg-0.2%Fe alloy. A maximum elongation of similar to 460% was attained in the Al 2024 alloy at 400 degreesC with an initial strain rate of 10(-3) s(-1). It is demonstrated that the ECAP can be effective in producing superplastic materials

Low-temperature superplasticity in a Cu-Zn-Sn alloy processed by severe plastic deformation

A copper alloy containing 38% Zn and 3% Sn was subjected to severe plastic deformation at a temperature of 400°C using the procedure of equal-channel angular pressing (ECAP). The microstructures produced by ECAP were relatively heterogeneous with areas of both recrystallized and unrecrystallized grains. Within the recrystallized areas, the average grain size was 1.5?m. Tensile testing after ECAP revealed the occurrence of superplasticity with elongations up to 900%. Superplastic ductilities were recorded at temperatures as low as 300°C corresponding to an homologous temperature of 0.51Tm, where Tm is the absolute melting temperature of the alloy. These results demonstrate the potential for achieving low temperature superplasticity in this alloy through ECAP. As in conventional superplastic Cu-based alloys, specimens failed because of the development of internal cavities