H13 steel is a widely used hot work die material. A new type of hot working method is imperative to develop complex and precise dies. In this paper, the heat treatment of H13 steel (AISI) was carried out by annealing, the final structure is a point or spherical pearlite, and the grain size is about 30–40 μm. The tensile properties of the annealed microstructure were investigated at 650, 750, and 850 °C with the strain rates of 1 × 10−3 s−1, 5 × 10−4 s−1, and 1 × 10−4 s−1. The tensile fracture and microstructure were analyzed by SEM and HREM. The results show that the tensile samples reach superplasticity at the strain rate of 1 × 10−4 s−1 in the temperature range of 750–850 °C. When the temperature is 850 °C, the maximum elongation rate reaches 112.5%. This demonstrates the possibility of making superplastic forming molds. During the tensile process, the refined M23C6 and other high hardness carbides which are dispersed uniformly in the matrix, effectively inhibits grain growth and hinders dislocation movement, leading to the improvement of plasticity.

Equiaxed ultrafine duplex alloys γ-TiAl and α2-Ti3Al are prepared by high-energy milling and hot pressing sintering. Microstructures presenting in the mixed and sintered powders are studied by scanning electron microscopy. Structural characteristics are investigated by high-resolution electron microscopy before and after compression at 1100–1200°C. The data reveal grain sizes of 300–500 and ∼100 nm for sintered γ-TiAl and α2-Ti3Al alloys, respectively. High deformation temperatures and low strain rates lead to low peak flow stress, and at such conditions the α2/γ and α2/α2 interfaces are prone to forming dislocation structure. The studies also reveal the presence of large-angle grain boundaries for the [Formula: see text] and (0002)α2/(0002)α2 interfaces.

Abstract:In this paper, the equiaxed superfine/nanocrystalline duplex PM-TiAl-based alloy with (γ + α 2 ) microstructure, Ti-45Al-5Nb (at %), has been synthesized by high-energy ball milling and vacuum hot pressing sintering. Superplastic deformation behavior has been investigated at 1000 • C and 1050 • C with strain rates from 5 × 10 −5 s −1 to 1 × 10 −3 s −1 . The effects of deformation on the microstructure and mechanical behaviors of high Nb containing TiAl alloy have been characterized and analyzed. The results showed that, the ultimate tensile strength of the alloy was 58.7 MPa at 1000 • C and 10.5 MPa at 1050 • C with a strain rate of 5 × 10 −5 s −1 , while the elongation was 121% and 233%, respectively. The alloy exhibited superplastic elongation at 1000 and 1050 • C with an exponent (m) of 0.48 and 0.45. The main softening mechanism was dynamic recrystallization of γ grains; the dislocation slip and γ/γ interface twinning were responsible for superplastic deformation. The orientation relationship of γ/γ interface twinning obeyed the classical one: (001) γ //(110) γ .

Abstract. According to the performance requirements of brake friction plate in the high speed train, Cu-based friction material was prepared by powder metallurgy technology. The friction components are mainly atomized Fe, a small amount of Cr and SiO2. And a high coefficient is caused by the friction resistance of these particles in the friction surface. The graphite forms a layer of solid lubricating film on the friction surface to ensure a stable friction coefficient under the all kinds of friction conditions. The compressive strength of sintered samples were tested by DDL50 Electronic Universal Testing Machine, and the property of dry friction and wear were tested by vertical universal friction-wear testing machine. The wearing morphologies were observed by SEM and the effects of friction speed on wear rate and friction coefficient were analyzed. The result shows that Cu-based containing larger natural flake graphite and smaller Fe particles has good friction wear performance. And when the load varying from 50N to 150N at the speed of 600r/min, the friction coefficient is about 0.4~0.48, the coefficient varies little and is very stable. The main wear mechanisms are abrasive wear and oxidation wear.