Investigation of specimen size effects by in-situ microcompression of equal channel angular pressed copper

Abstract

a b s t r a c tMicropillar compression testing was implemented on Equal Channel Angular Pressed copper samples ranging from 200 nm to 10 mm in side length in order to measure the mechanical properties yield strength, first load drop during plastic deformation at which there was a subsequent stress decrease with increasing strain, work hardening, and strain hardening exponent. Several micropillars containing multiple grains were investigated in a 200 nm grain sample. The effective pillar diameter to grain size ratios, D/d, were measured to be between 1.9 and 27.2. Specimens having D/d ratios between 0.2 and 5 were investigated in a second sample that was annealed at 200°C for 2 h with an average grain size of 1.3 mm. No yield strength or elastic modulus size effects were observed in specimens in the 200 nm grain size sample. However work hardening increases with a decrease in critical ratios and first stress drops occur at much lower stresses for specimens with D/d ratios less than 5. For comparison, bulk tensile testing of both samples was performed, and the yield strength values of all micropillar compression tests for the 200 nm grained sample are in good agreement with the yield strength values of the tensile tests.

Cryogenic Stress-Driven Grain Growth Observed via Microcompression with in situ Electron Backscatter Diffraction

“…The schedule consists of a large plastic load, followed by several elastic loadings of 400 lN, and a final plastic load. The elastic loads of 400 lN correspond to a stress of 82 MPa in the microcompression specimen, which is well below the yield stress of 383 ± 34 MPa obtained from room-temperature microcompression testing 24 ; a cryogenic stress-strain curve is presented in Supplementary Fig. S1.…”

“…The material used in this investigation was ECAP, ultrahigh-purity, ultrafine-grained copper, which has 15% 50 nm to 200 nm dislocation-free grains, 37% 100 nm to 200 nm grains with chaotically distributed dislocations, and 48% 100 nm to 500 nm grains with subboundaries. 24 ECAP copper was chosen for this work due to its ultrafine grain structure that (1) permits a larger number of grains in a microscale compression test 24 and (2) allows for multiple grains to be present on the surface for EBSD characterization. The ECAP material originated from a 25-mm-diameter rod.…”

“…A full description of the processing, often described as route Bc in ECAP literature, can be found in Ref. 24.…”

Enhanced strength and ductility of AZ80 Mg alloys by spray forming and ECAP

“…Severe plastic deformation (SPD) techniques, such as equal channel angular pressing (ECAP), have been effectively used to refine the overall microstructure of copper [16,17], aluminum [18], titanium [19], nickel [20], Mg [21] and other metals [22,23]. In the case of hcp metals such as Mg, ECAP processing has been reported to have the following effects.…”

The influence of microstructure on the cyclic deformation and damage of copper and an oxide dispersion strengthened steel studied via in-situ micro-beam bending

“…As test materials, copper and an oxide dispersion strengthened (ODS) steel were examined, both as single grained micro-beams and the copper as a micro-beam with a refined microstructure smaller than the sample size due to severe plastic deformation processing. Copper is an especially interesting material to evaluate this new technique due to the fact that data from many uniaxial small scale mechanical testing techniques is available for copper, and it serves as a good benchmarking material [10,[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47].…”