Hardening (metallurgy)

About: Hardening (metallurgy) is a research topic. Over the lifetime, 25584 publications have been published within this topic receiving 376012 citations.

Identification of optimum binder phase compositions for improved WC hard metals

Abstract: The possibility has been investigated of using measurements of the mechanical properties of alloys with binder phase compositions to identify binder phases that will provide high hardness and toughness in WC hard metals based on cobalt, nickel, CoNi, NiAl, NiCrMo and NiCrMoAl. The results showed that, in WCCo and WC(CoNi) hard metals with constant grain size and binder phase content, an optimum grain size and binder phase content, an optimum combination of fracture toughness and compressive strain could be obtained at particular tungsten and carbon contents which could be determined from measurements of magnetic saturation and lattice parameters. As predicted from tests on NiWC alloys, it was found that WCNi hard metals had lower toughness and strength than WCCo hard metals do. Additions of aluminium to nickel binder phases to form γ′ precipitates raised the strength and conferred creep resistance but decreased the fracture toughness. Solid solution strengthening by chromium and molybdenum raised the hardness without reducing toughness as measured by Palmqvist tests and gave properties which matched those of WCCo hard metals. By combining γ′ hardening and solid solution hardening by chromium and molybdenum in nickel-based binder phases, better values of hardness and toughness were obtained than those of WCCo hard metals. The new compositions also offered the possibilities of enhanced resistance to creep and corrosion, and properties that could be varied by heat treatments to meet specific requirements.

Hierarchically structured diamond composite with exceptional toughness

Abstract: The well known trade-off between hardness and toughness (resistance to fracture) makes simultaneous improvement of both properties challenging, especially in diamond The hardness of diamond can be increased through nanostructuring strategies1,2, among which the formation of high-density nanoscale twins - crystalline regions related by symmetry - also toughens diamond2 In materials other than diamond, there are several other promising approaches to enhancing toughness in addition to nanotwinning3, such as bio-inspired laminated composite toughening4-7, transformation toughening8 and dual-phase toughening9, but there has been little research into such approaches in diamond Here we report the structural characterization of a diamond composite hierarchically assembled with coherently interfaced diamond polytypes (different stacking sequences), interwoven nanotwins and interlocked nanograins The architecture of the composite enhances toughness more than nanotwinning alone, without sacrificing hardness Single-edge notched beam tests yield a toughness up to five times that of synthetic diamond10, even greater than that of magnesium alloys When fracture occurs, a crack propagates through diamond nanotwins of the 3C (cubic) polytype along {111} planes, via a zigzag path As the crack encounters regions of non-3C polytypes, its propagation is diffused into sinuous fractures, with local transformation into 3C diamond near the fracture surfaces Both processes dissipate strain energy, thereby enhancing toughness This work could prove useful in making superhard materials and engineering ceramics By using structural architecture with synergetic effects of hardening and toughening, the trade-off between hardness and toughness may eventually be surmounted