Strain dependent grain growth during cold rolling deformation of gradient nanograined nickel

The effect of the rolling strain on grain growth behavior of two gradient nanograined nickel samples (average grain size ranging from 20~90nm) with symmetrical structure was investigated by scanning electron microscope/transmission electron microscopy observation, X-ray line profile analysis and microhardness measurement. In both gradient microstructures, under the same volume fraction, the layer with small grains and the layer with large grains was systematically compared. Quantitative analysis indicated that at a given nominal rolling strain small grains seem to grow more slowly than large grains, which can be attributed to the fact that the “hard” small grains sustain less deformation when the gradient are deformed to a certain strain.

Effect of Rolling Strain on the Mechanical and Tribological Properties of 316 L Stainless Steel

The mechanical and tribological performances of 316 L stainless steel subjected to different cold rolling (CR) strains were investigated. The microhardness and strength of 316 L stainless steel were improved attributed to the formation of high-density defects, such as dislocations and parallel lamellar structures. Furthermore, the tribology tests were conducted under dry sliding at room temperature. With the increase in rolling strain, the wear rate of 316 L stainless steel gradually decreased due to the improvements in microhardness and strength. For the as-received specimen, the strong adhesive wear leads to the maximum wear rate compared with the cold rolled specimens. Under higher rolling strain conditions, the grain boundary embrittlement caused by oxygen reaction leads to the formation of oxidative abrasive under dry sliding conditions, and then the oxidative abrasive could serve as the third body at the siding interface. Consequently, there is a transition phase where the wear mechanism gradually shifts from adhesive to abrasive wear.

Effect of Cold Rolling and Heat Treatment on Properties and Microstructure of Cu-24wt%Ag Alloys

Sheets of Cu-24wt.%Ag alloy were prepared through the process of forging, cold rolling and heat treatment to reveal the evolution of microstructures, mechanical properties and electrical conductivity. The experimental results showed that nanomultilayered structure of Cu and Ag phases arranged alternatively was obtained, with numerous nanoscale Ag precipitate-fibers embedded in Cu matrix. The lamellas in longitudinal section became curved gradually and shear bands appeared when the deformation exceeded 90.79%. With the increase of rolling strain, the average layer thickness and spacing decreased progressively and reached to less than 200 nm as the strain surpassed 96%, resulting in rapid enhancement of the hardness. The heat treatment at 250°C markedly improved electrical conductivity of the alloy, with little decline of the hardness. The anisotropy of the alloy reduced with rising temperature. Local spheroidization occurred when the alloy was heat treated at 300°C. Hardening of this Cu-Ag alloy is predominated by Cu/Ag interface in strain stage of 80%~99%, leaning mainly upon layer thickness and spacing.

Anomalous Strain Rate Sensitivity of Nanocrystalline Ni Induced by Rolling Deformation

The strain rate sensitivity of rolled nanocrystalline (NC) Ni was studied by nanoindentation. The grain continuously grows from 20 nm to 92 nm after rolling deformation. The stress driven grain boundary migration accompanied by dislocation emission leads to the grain growth. The strain sensitivity first increase and then decrease with the increased rolling strain, which has a similar variation of dislocation density in rolled NC Ni. The remarkable shift of rate sensitivity is attributed to the dislocation supported grain boundary mediated process.