Dušan Božić

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.

Effect of synthesis parameters on structural and mechanical properties of Ti 3 Al–Nb–Mo intermetallic compound obtained by powder metallurgy techniques

The influence of microstructure, heat treatment and alloying addition on mechanical and fracture properties of Ti3Al-based intermetallic at room and elevated temperatures was studied. Ti3Al–11Nb–1Mo (mole fraction, %) alloy was consolidated via powder metallurgy processing by mechanical alloying (MA) and hot pressing (HP). MA powders were characterized using XRD and SEM-EDS. Optimum MA duration was 25 h and HP conditions of 1350 °C, 2 h, 35 MPa. After HP, solution treatment at 1050 °C for 1 h and water quenching α2+β Widmanstatten microstructure is present, while subsequent aging at 800 °C during 24 h induces small content of O-phase. High fraction of β-phase is a direct consequence of Mo. Compression tests were performed from room temperature to 750 °C in vacuum. The yield strength of compacts increases with temperature up to 250 °C (pyramidal slip systems activation), after which it decreases. Ductility increases throughout the whole temperature range. The presence of O phase contributed to ductility increase in aged alloys, while negligibly lowering yield strength. Registered drop in the yield strength of aged alloys compared with non-aged ones was mostly influenced by precipitation of α″2 particles. Mixed fracture modes are operative at all temperatures.

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.

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.