The formation of friction-induced nanocrystalline structure in submicrocrystalline Cu–Cr–Zr alloy рrocessed by DCAP

Abstract

The paper studies the effect of high strain rate (10 5 s −1) deformation by the method of dynamic channel-angular pressing (DCAP), annealing and quasi-static severe plastic deformation (SPD) under sliding friction on the evolution of the structure and properties of low-alloyed dispersion-hardened Cu-Cr-Zr alloys. It is shown that alloying of copper with chromium (0.09-0.14 %) and zirconium (0.04-0.08 %) microadditives changes mechanisms of submicrocrystalline (SMC) structure formation and elastic energy relaxation during DCAP: the cyclic character of structure formation associated with alternating of high-rate processes of fragmentation and dynamic recrystallization is changed to processes of fragmentation and partial strain aging resulting in precipitation of nanosized particles of the second-phase. The temperature-time regime of annealing (aging) of Cu-Cr-Zr SMC alloys processed by DCAP was established to improve the mechanical properties and electrical conductivity. In particular, for Cu-0.14 Cr-0.04 Zr SMC alloy it was shown that the optimal combination of microhardness (HV = 1880 MPa), electrical conductivity (80 % IACS), strength (σ 0.2 = 464 MPa, σ u = 542 MPa) and ductility (δ = 11 %) can be obtained by DCAP and aging at 400°C for 1 h. The improved mechanical properties of the alloys as compared to copper are associated with extra hardening caused by precipitation of Cu 5 Zr and Cr nanoparticles (5-10 nm) in the process of DCAP and aging. It was shown that low-alloyed Cu-Cr-Zr alloys possessed a high work-hardenability due to the methods of DCAP and SPD under sliding friction. By the example of Cu-0.09 Cr-0.08 Zr alloy it was established that the wear rate of samples with SMC structure obtained by the DCAP method decreased by a factor of 1.4 as compared to the coarse-grained state. It was also established that the combination of the treatment by DCAP, aging at 400°С, and SPD under friction of the alloy resulted in the formation of the friction-induced nanocrystalline structure with the grain size of 15-60 nm in the surface-layer material, which provided a high level of microhardness (3350 MPa) and low values of the friction coefficient (0.35).

Investigation of Cu5Zr particles precipitation in Cu-Zr and Cu-Cr-Zr alloys subjected to quenching and high strain rate deformation

“…DCAP of the alloys increases its microhardness up to 1400 and 1600 MPa, that is 2.3-fold as against the initial one (Fig. 5, curves 1 and 2), which is associated with a significant (from 300 -400 to 0.2 -0.4 μm) structure refinement and partial deformation aging in the process of DCAP [13,14]. Annealing of the deformed Cu-0.21 % Cr-0.20 % Zr alloy at temperatures of 300°C for 1 h (at 400°C for 1 h for the Cu-0.06 % Zr alloy) did not change their microhardness (Fig.…”

“…As it has been established earlier, after DCAP with n = 3 -4, a fragmented structure consisting of grains and sub-grains with a size of 0.2 -0.4 μm with the internal dislocation structure is formed in the alloys. Nanoparticles of the second-phase with a diameter from 2 to 5 nm are precipitated on the boundaries and inside individual crystallites, which suggests that a partial decomposition of the supersaturated α-solid solution of copper occurs in the process of DCAP [13,14]. Fig.…”

“…It is important to emphasize that, in the case of DCAP, the simple shear deformation, which produces the structure upon ECAP, is a high-strain-rate process; moreover, upon DCAP, a high-speed shock-wave compressive strain takes place, which creates an additional source of deformationinduced work hardening. It was previously established that the strength of precipitation-hardenable copper alloys with 0.2 -0.5 wt.% Cr and Zr can be additionally increased by optimizing the temperature-time parameters of postdeformation annealing [1][2][3][4][5]13,14]. The process of solid solution decomposition in Cu-Cr-Zr alloys has been investigated repeatedly [1-4,13 -16].…”

“…The Cu 5 Zr phase has a complex face-centered cubic lattice of the Be 5 Au type with a lattice parameter of 0.687 nm [1,4,14]. According to [1,4,16], the limited solubility of zirconium in copper at 967°С is 0.15 wt.%; 850°С is 0.073 wt.% and at 600°С -0.01 wt.%.…”

Wear-resistant nickel-based laser clad coatings for high-temperature applications

“…The samples with NiCrBSi coating were subjected to a two-body abrasive test over the fixed Al 2 O 3 corundum abrasive with a specific load p =1 MPa and average sliding speed V = 0.175 m / s. The tribological tests of the samples with NiCrBSi coatings were performed according to "pin-ondisk" scheme by sliding the coating surface over the Kh12M steel disk (wt.%: 1.5С-12Cr-0.5Mo-0.2V; hardness 61.5 HRC) with p = 2 MPa, V = 3.1, 4.7, 6.1 and 9.3 m / s, testing time t = 9.5 -30 min. The wear intensity was calculated by the method described in [10]. The tribological tests of NiBSi-WC coating were performed according to "pin-on-plate" scheme by reciprocation sliding the coating surface over the Kh12M steel plate with p = 6 MPa, V = 0.08 m / s, sliding distance L = 60 mm.…”