Effect of Ce content on mechanical properties of Ce/Cr coated open-cell Ni-Cr-Fe alloy foams

The Ce/Cr coating was homogenously deposited onto the reticulated open-cell Ni?Cr?Fe alloy foam by the pack cementation process.The mechanical properties of the Ce/Cr coated alloy foams were investigated by the quasi-static compression test.Simultaneously,the deformation and failure mechanisms of Ce/Cr coated alloy foams were discussed.The results show that the adding amount of CeO2powders influences the mechanical properties of the Ce/Cr coated alloy foams.Despite an increase in density as compared to the uncoated foams,the Ce/Cr coated foams exhibit improvement in both yield strength and energy-absorption performance.Especially,the energy-absorption performance of2%Ce/Cr(mass fraction)coated alloy foam is averagely1.9times as high as that of the bare Ni?Cr?Fe alloy foam.In addition,the mechanical properties of the Ce/Cr coated alloy foams increase with the increase of strain rate.The distortion and cracking are mainly the deformation behavior of the Ce/Cr coated alloy foam,confirmed by SEM images.

Microstructure and mechanical properties of friction stir welding joint during post weld heat treatment with different zigzag lines

Zigzag line is a common defect in friction stir welding(FSW) joint.The formation mechanism of the zigzag line in Al-Cu alloy FSW joint and its influence on the microstructure and mechanical properties during post weld heat treatment(PWHT) were studied by scanning electron microscopy(SEM),microhardness and tensile tests.It is found that the occurrence of zigzag line for PWHT joint is determined by PWHT process which in nature depends on residual stress and thermal stress of FSW joint.The optimization of PWHT process to reduce the residual and thermal stress can trigger for the deterioration of mechanical properties of PWHT joints with zigzag line.No obvious decrease of tensile properties is observed for T6-450 and T6-495 joints although zigzag line appears in the weld.PWHT determines the sizes of zigzag line cracks and consequently determines the fracture location and characteristics of FSW joint.

Mechanical behaviors and energy absorption properties of Y/Cr and Ce/Cr coated open-cell nickel-based alloy foams

In this study, Y-and Ce-modified Cr coatings applied by pack cementation method were prepared on the surface of open-cell nickel-based alloy foam. The morphologies and microstructures of Y- and Ce-modified Cr coatings with various Y and Ce contents were investigated in detail. Then, the effects of Y and Ce addition on the mechanical properties of open-cell nickel-based alloy foams were analyzed and compared. Simultaneously, the energy absorption capacity and energy absorption efficiency of the Y- and Ce-modified Cr coated alloy foams were discussed and compared at the room and high temperatures. The results show that Cr coatings containing minor amounts of rare earth element （Y and Ce） are well adhered to the nickel-based foam struts. Especially, the microstructure of the 2 wt% Ce-modified Cr coating is denser and uniform. In addition, the compressive strength and plateau stress of Y- and Ce-modified Cr coated alloy foams firstly increase and then decrease by increasing the Y and Ce contents at room and high temperatures. The energy absorption capacity of Y/Cr and Ce/Cr coated alloy foams increases linearly with the strains increasing. The Ce/Cr coated alloy foams can absorb more energy than Y/Cr coated alloy foams in the plateau and densification regions at room temperature. Compared to those at room temperature, the Y- and Ce-modified Cr coated alloy foams show higher energy absorption efficiency when deforma- tion within 10%-30% at high temperature.