Viseslava Rajkovic

The influence of microstructural characteristics and contaminants on the mechanical properties and fracture topography of low cost Ti6Al4V alloy

Abstract Low cost titanium alloy compacts were produced via the powder metallurgy approach through the hydride – dehydride process and hot consolidation (hot pressing and hot isostatic pressing). The conditions of the reversible hydride – dehydride process were determined by X-ray and scanning electron microscopy characterisation of powders. Powders were consolidated both above and below the β transformation temperature. The morphology of the microstructure, and the presence of open and closed pores, as well as residual particles of hydrides and oxides have a direct influence on the mechanical properties of compacts (tensile properties and impact toughness).

Properties of copper composites strengthened by nano- and micro-sized Al2O3 particles

Abstract Electrolytic copper powder, inert gas atomized prealloyed copper powder containing 3.5 wt.% Al, and a mixture of copper and commercial Al2O3 powder particles (4 wt.% Al2O3) were milled separately in a high-energy planetary ball mill for up to 20 h in air. The milling was performed in order to strengthen the copper matrix by grain size refinement and Al2O3 particles. Milling in air of prealloyed copper powder promoted formation of fine dispersed Al2O3 particles by internal oxidation. Hot-pressing (800 °C for 3 h in argon at a pressure of 35 MPa) was used for compaction of milled powders. Compacts from 5 and 20 h milled powders were additionally subjected to high temperature exposure (800 °C for 1 and 5 h in argon) in order to examine their thermal stability and electrical conductivity. The effect of different size and the amount of Al2O3 particles on strengthening, thermal stability and electrical conductivity of the copper-based composites was studied. The results were discussed in terms of the effects of the grain size refinement along with micro- and nano-sized Al2O3 particles on the strengthening of the copper matrix.

Synthesis and characteristics of precipitation hardened Cu–Cr alloy and multiply hardened Cu–Cr–Al2O3 nanocomposite obtained using powder metallurgy techniques

Abstract The hardening of copper alloy by using powder metallurgy techniques and analysis of its effects on the strength of obtained material are discussed. Prealloyed Cu-0.5 wt.% Cr powder and mechanically alloyed Cu-0.5 wt.% Cr-3 wt.% Al2O3 powder were consolidated by means of hot pressing. Optical microscopy, scanning electron microscopy and transmission electron microscopy were used for microstructure characterization of compacts. Hardness and electrical conductivity of both compacts were compared. High strengthening of the Cu–Cr compacts is achieved by aging as a consequence of the influence of precipitation particles rich in chromium. In the case of the Cu–Cr–Al2O3 composite it is a consequence of precipitation of particles rich in chromium and the presence of Al2O3 dispersoid nanoparticles.

Microstructural and mechanical properties of Cu-7vol.%ZrB2 alloy produced by powder metallurgy techniques

Abstract The Cu-7vol.%ZrB2 alloy examined in this study was consolidated via powder metallurgy (PM) processing by combining mechanical alloying and hot pressing. Powder mixture with composition: 94.78 wt.% copper, 4.1 wt.% zirconium, and 1.12 wt.% boron was used as a starting material. Mechanical alloying of powder mixture was performed at various times: 5, 10, 15, 20, 25, and 30 h. Structural changes that occur in the samples of copper alloy with 7vol.%ZrB2 after milling and during hot pressing process were studied with the use of X-ray diffraction. Scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectrometry (EDS) was applied to examine the morphological properties and elemental analysis of the hot-pressed samples as a function of milling times. Also, hardness of the Cu-7vol.%ZrB2 alloy was investigated, and the results showed that hardness of the samples increased as the milling time increased. The compressive properties at room temperature are correlated to the corresponding hardness results. Distribution of ZrB2 particles and presence of agglomerates in the Cu matrix directly depend on the milling time and show strong influence on compressive properties and fracture of Cu-7vol.%ZrB2 alloy.

Properties of Copper-Based Composite Reinforced with Al2O3 Particles of Different Size

Copper matrix was simultaneously reinforced with nano- and micro-sized Al2O3 particles via high-energy milling of the mixture of inert gas-atomized prealloyed Cu-1 wt.% Al powder and 0.6 wt.% commercial Al2O3 powder. At the maximum of microhardness (2400 MPa) the grain size reaches the smallest value as a result of the synergetic effect of nano- and micro-sized Al2O3 particles. The relatively low decrease in microhardness during HTE may be explained by grain growth which is retarded by Al2O3 nano-sized particles precipitated at the grain boundaries.

Structural and mechanical characteristics of za27-7 wt.% SiC composites produced by powder metallurgy techniques

Abstract This paper describes a study of the structural and mechanical properties of Zn-matrix composites discontinuously reinforced by 7 wt.% SiC particles of size 0.7 μm. Commercial Zn-rich Zn–Al–Cu (ZA27) alloy was gas atomized, the resulting powder was mixed with a SiC powder and hot compacted into cylindrical pellets. Metal powder and powder mixture were pressed at 230°C for 60 min, under a pressure of 170 MPa. The compressive strength testing was performed in the temperature range from 20°C to 170°C with a deformation rate of 2.4 × 10–3 s–1. Detailed microstructure characterization of samples has been evaluated by optical and scanning electron microscopy.