Hardening (metallurgy)

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

Deformation microstructures, strengthening mechanisms, and electrical conductivity in a Cu–Cr–Zr alloy

Abstract: The ultrafine-grained microstructures, mechanical properties and electrical conductivity of a Cu–0.87%Cr–0.06%Zr alloy subjected to multiple equal channel angular pressing (ECAP) at temperatures of 473–673 K were investigated. The new ultrafine grains resulted from progressive increase in the misorientations of strain-induced low-angle boundaries during the multiple ECAP process. The development of ultrafine-grained microstructures is considered as a type of continuous dynamic recrystallization. The multiple ECAP process resulted in substantial strengthening of the alloy. The yield strength increased from 215 MPa in the original peak aged condition to 480 MPa and 535 MPa after eight ECAP passes at 673 K and 473 K, respectively. The strengthening was attributed to the grain refinement and high dislocation densities evolved by large strain deformation. Modified Hall–Petch analysis indicated that the contribution of dislocation strengthening to the overall increment of yield stress (YS) through ECAP was higher than that of grain size strengthening. The formation of ultrafine grains containing high dislocation density leads to a small reduction in electrical conductivity from 80 to 70% IACS.

Precipitation process and effect on mechanical properties of Mg–9Gd–3Y–0.6Zn–0.5Zr alloy

Abstract: Precipitation process and its effect on the Vickers hardness, room temperature tensile properties of Mg–9Gd–3Y–0.6Zn–0.5Zr (GWZ930) alloy were investigated in combination with differential scanning calorimetric (DSC), transmission electron microscopy (TEM), Vickers hardness and room temperature tensile test. A four-stage precipitation sequence of supersaturated Mg solid solution, Mg(SSSS) → β″ (144 °C) → β′ (240 °C) → β1 (276 °C) → β (stable), was analyzed. A satisfied combination of high rupture tensile strength and ductility was obtained when the alloy was aged at 200 °C for 63 h post extrusion. Moreover, the effective strengthening mechanisms were explicitly considered and the model prediction strength of GWZ930 alloy was proposed. It is concluded that precipitate strengthening due to the sub-micron metastable phases of β″ and β′ was the largest contributor to the room temperature tensile strength of the alloy GWZ930.

The effect of solution heat treatment and quenching rates on mechanical properties and microstructures in AlSiMg foundry alloys

Abstract: Four common AlSiMg foundry alloys have been solution heat treated at 813 K, quenched, and immediately aged at 423 K for up to 240 minutes. The mechanical properties are found to be related to the amount of Mg and Si in the alloys. A high strength is obtained after only 60 minutes of solution heat treatment, indicating that the solid solution is rapidly saturated on Mg and Si. The ductility is very much related to the amount of silicon present and the refinement of the silicon crystals within the eutectic areas, since silicon crystals are observed to crack when load is applied. Thus, a well-modified structure is the best way to obtain high ductility. Reduced quencing rates after solution heat treatment lead to a lower strength, since a lower number of hardening β′-Mg2Si precipitates are formed. The ductility of alloys with 0.6 wt pct Mg is increased with a reduced quenching rate. A more ductile matrix corresponding to the lower amount of hardening precipitates can explain this. Alloys with 0.2 wt pct Mg remain relatively unchanged. A hypothesis that may explain this phenomenon is the precipitation of brittle silicon or formation of coarse Mg2Si within the dendrites.

Hardening Shrinkage and Hygroscopic Expansion of Composite Resins

Abstract: Polymerization shrinkages of various restorative resins were measured. The specimens stored in water expanded, but most did not recover sufficiently to countervail the losses from polymerization.