In-situ Processing of TiB2 Nanoparticle-Reinforced Copper Matrix Composites

In order to produce the composite powder analyzed in this paper, two prealloys were melted and afterwards gas atomized. The obtained TiB2-reinforced copper powder was consolidated by hot isostatic pressing (HIP). Since it is known that a decrease in the size of the reinforcing phase can cause an increase in hardness of composites, the main aim of the experimental work was to obtain as small particles of the dispersed phase as possible by using standard powder metallurgy techniques. Microstructure and microhardness of the as-cast prealloys, as-atomized powder and HIP-ed compacts were examined. The results of these examinations revealed that TiB2 particles about 10 nm in size were in-situ formed and homogenously dispersed in the copper matrix. As a consequence of the TiB2 formation, the microhardness of Cu-TiB2 composite was significantly improved

The combination of precipitation and dispersion hardening in powder metallurgy produced Cu-Ti-Si alloy

Microstructure and microhardness properties of precipitation hardened Cu-Ti and precipitation/dispersion hardened Cu-Ti-Si alloys have been analyzed. Cu-1.2Ti and Cu-1.2Ti-3TiSi(2) (wt.%) atomized powders were characterized before and after consolidation by HIP (Hot Isostatic Pressing). Rapidly solidified powders and HIP-ed compacts were subsequently subjected to thermal treatment in hydrogen at temperatures between 300 and 600 degrees C. Compared to Cu-Ti powder particles and compacts, obtained by the same procedure, the strengthening effect in Cu-1.2Ti-3TiSi(2) powder particles and compacts was much greater. The binary and ternary powders both reveal properties superior to those of Cu-1.2Ti and Cu-1.2Ti-3TiSi(2) compacts. Microhardness analysis as a function of the aging temperature of Cu-1.2Ti-3TiSi(2) alloy shows an interaction between precipitation and dispersion hardening which offers possibilities for an application at elevated temperatures. (C) 2007 Elsevier Inc. All rights reserved

Mechanical and fracture behavior of powder metallurgy processed Ti3Al-based alloys

This work considers structural and compression mechanical properties of three Ti3Al-based alloys processed by powder metallurgy. Mechanically alloyed powders were compacted by hot-pressing to non-porous homogenous compacts. Prior to compression tests, all compacts were homogenized by a solution treatment at 1050 degrees C (alpha + beta region) for 1h, followed by water quenching. The compression tests were performed from room temperature to 500 degrees C in vacuum at a strain rate of 2.4 x 10(-3) s(-1). Detailed microstructural characterization has been evaluated by scanning electron microscopy (SEM), followed by electron dispersive spectroscopy (EDS) and X-ray diffraction analysis. Fracture topography was examined by SEM. The Ti3Al-Nb alloy exhibits the highest ductility in the whole temperature range, whereas addition of Mo to Ti3Al-Nb alloy yields the highest ultimate compression strength. A correlation between ductility and the fracture mode exists for all materials. (c) 2006 Springer Science + Business Media, Inc

Modeling of densification process for particle reinforced composites

It is a well known fact that behavior of materials during consolidation at high temperatures is a very complex issue. Each mechanism that promotes densification, depends on a large number of parameters in many different ways, making the development of the densification process very difficult to plan. For that reason, any kind of model which could encompass large number of the influencing parameters would be a great contribution for easier planning and handling of the densification process. Modeling of densification process based on the papers of well-known authors, including a new appropriate modifications is presented in this work. Importance of this model is that it can be applicable to composite materials. This new model was tested on a real Al-SiC composite systems (Al-10 vol.% SiC, Al-30 vol.% SiC and Al-50 vol.% SiC). Predicted behavior of composites obtained by model calculations and the one defined through the experiments concur in the 7-30% range. (C) 2009 Elsevier B.V. All rights reserved

Influence of SiC particles distribution on mechanical properties and fracture of DRA alloys

In the last 20 years a new class of metal matrix composite material (DRA - Discontinuously Reinforced Aluminum) with aluminum alloy matrix and Sic particles as secondary phase has been developed. The most important step during composite production is the homogenization process of metal and ceramic powder particles. Quantitative analysis of a SiC particles distribution in the aluminum alloy matrix (CW67) was used to determine the optimum homogenization parameters of different powders. It was found out that the level of mixture homogeneity largely depends on the amount of mixing dish filling, homogenization time and characteristics of reinforcing particles. By introducing the concept of homogeneity index, it was shown that the lowest values of the mentioned parameter correspond to the best uniformity of Sic particles in the CW67 matrix. Composite with the lowest value of homogeneity index was the one with 5 vol.% of SiC, homogenized during 60 min and the amount of mixing dish filling of 20 vol.%. This composite displayed the best values of mechanical properties and fracture resistance. (C) 2009 Elsevier Ltd. All rights reserved

Application of ANOVA method to precipitation behaviour studies

The Analysis of variance (ANOVA) method has been used to illustrate the implementation of adaptive numerical (AN) techniques for the prediction of the precipitation behaviour of commercial materials. Case studies involving the analysis of a-phase precipitation kinetics in duplex stainless steel (DSS) produced by sand casting and age hardening of 2219 alummium alloy microalloyed with Ge and/or Si are presented. For each alloy, complex datasets comprised the results obtained from heat treatment trials on a range of commercial processing conditions, so that a single and combined effect of various parameters can be determined. This enabled an estimate of the most influential parameters to be made, providing an effective means of commercial alloy development and process optimisation. (c) 2005 Elsevier B.V. All rights reserved

Rietveld refinement of crystal phases (Ca1-xLax)MnO3 with perovskite-type structure

Two nanopowders with nominal compositions (Ca0.7La0.3)MnO3 (CLM) and (Ca0.7La0.3)(Mn0.8Ce0.2)O-3 (CLMC) were synthesized by a modified glycine/nitrate procedure. XRD analysis revealed binary phase mixture in both samples. The influence of La and Ce on unit cell parameters, atom positions, and average bond distances were analyzed. According to these results and refined occupation factors of La and Ca, as well as quantitative phase analysis it was found that the CLM sample consists of 85 mass.% of Ca0.62La0.38MnO3 and 15 mass.% of Ca0.99La0.01MnO3, while the CLMC sample consists of 70 mass.% of Ca0.58La0.42MnO3 and 30 mass.% of CeO2. Microstructure size-strain analysis was performed and the Rietveld refinement gave crystallites of about 100 angstrom. TEM images showed particle sizes of about 100-500 angstrom.Research Trends in Contemporary Materials Science, 8th Conference of the Yugoslav-Materials-Research-Society (Yu-MRS), Sep 04-08, 2006, Herceg Novi, Montenegr

Influence of retained hydride particles and microstructure on mechanical properties of PM produced Ti-6Al-4V alloy

Compacts of Ti-6Al-4V alloy were produced via the powder metallurgy technique applying the hydride-dehydride process and hot isostatic pressing. The conditions of reversible hydride-dehydride process were controlled by chemical and X-ray diffraction analysis and scanning electron microscopy. Powders were pressed above and below the alpha - GT beta transus temperature. The presence of titanium hydrides and morphology of the microstructure have the direct influence on the tensile properties and fracture toughness of the Ti-6Al-4V alloy, but the effect of microstructure is more pronounced

Microstructure and mechanical properties of precision cast TiAl turbocharger wheel

From a technical perspective, many of the unique properties of TiA1-based alummides making them attractive for high-temperature structural application also assign these alloys a challenge to process into useful products. Cast TiA1 alloys due to their relatively low production cost are on the verge of a commercial application, especially in vehicle industry. The results concerning technology of precision casting together with microstructural and mechanical tests examinations of a turbocharger TiAl-based wheel prototype have been described. The processing technology of self-supporting ceramic shell molds was successfully verified during precision casting of turbocharger wheels. According to all results, a processing window for precision casting was established. (c) 2005 Elsevier B.V. All rights reserved

Structural and mechanical characteristics of ZA27-7 wt.% SiC composites produced by powder metallurgy techniques

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 mum. 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 degreesC for 60 min, under a pressure of 170 MPa. The compressive strength testing was performed in the temperature range from 20 degreesC to 170 degreesC with a deformation rate of 2.4 x 10(-3)s(-1). Detailed microstructure characterization of samples has been evaluated by optical and scanning electron microscopy