Papers by Keyword: Vacuum Hot Pressing

Abstract: In the present study, Cu₆₀Zr₃₀Ti₁₀ metallic glass powders were prepared by mechanical alloying of pure Cu, Zr, and Ti powder mixtures. Cu₆₀Zr₃₀Ti₁₀ metallic glass composite powders were obtained after 5 h of milling as confirmed by X-ray diffraction and transmission electron microscopy. The metallic glass powders were found to exhibit a supercooled liquid region before crystallization. Cu₆₀Zr₃₀Ti₁₀ bulk metallic glass were synthesized by vacuum hot pressing the as-milled Cu₆₀Zr₃₀Ti₁₀ metallic glass powders at 723 K in the pressure range of 0.72 ~ 1.20 GPa. Cu₆₀Zr₃₀Ti₁₀ BMG with nanocrystalline precipitates homogeneously embedded in a highly dense glassy matrix was successfully prepared under applied pressures. It was found that the pressure could enhance the thermal stability and prolong the existence of amorphous phase inside Cu₆₀Zr₃₀Ti₁₀ powders.

Abstract: Machining of Aluminum Metal Matrix Composites (AMMCs) is a challenge for manufacturing industries due to their heterogeneous constituents which vary from soft matrix to hard reinforcements and their interfaces. To overcome the difficulties in machining of MMCs, researchers are continuously working to find the optimum process or machining parameters. In this work, End milling studies were carried out in A356 alloy powder-SiC particles (1 μm) in 0, 5, 10, 15 volume % reinforced AMMCs synthesised by vacuum hot pressing (VHP) route.The influence of machining parameters such as cutting speed, feed and depth of cut on the prepared composites in terms of surface roughness (Ra) and material removal rate (MRR) are measured from experimental study. Experiments were conducted as per Taguchi L₁₆ orthogonal array with 4 factors and 4 levels.From the experimental result, it was identified that surface roughness varied from 0.214 μm to 4.115 μm and MRR varied from minimum of 1.11 cm³/min to maximum of 9.65 cm³/min. It is also observed that, MRR increased with increase in machining parameters and reinforcement quantity. Similarly, surface roughness decreased for increase of cutting speed, SiC particle (SiC_p) reinforcement and increased for increase in feed and depth of cut. The optimum condition were observed in higher speed, lower feed and higher depth of cut on MMC with higher SiC content (15%) for getting higher machinability.

Abstract: Copper - multiwall carbon nanotubes (MWCNT) composite was processed by powder metallurgical processing technique. Pure copper powder and MWCNT were mechanically alloyed by high energy milling to produce Cu-MWCNT composite powder. The composite powder was subsequently consolidated by vacuum hot pressing. Characterization studies were conducted along axial (hot pressing direction) and radial (transverse) directions. Microstructural observations of the processed composite revealed random distribution of MWCNT in axial direction and aligned distribution in radial direction. The structure property correlation was established and it revealed certain degree of anisotropy in mechanical and electrical properties of the composite.

Abstract: The continuous progress of the electronic industries put forward a new requirement to the electronic components that must have an excellent heat conduction performance. Thus diamond-Cu composite is developed as a high thermal conductivity and low coefficient of thermal expansion material. A vacuum hot pressing method is chosen to prepare diamond-Cu composites and the thermal conductivity of the diamond-Cu composite is researched. The effects of different contents of chromium, the size of diamond particles and the content of diamond particles on the thermal conductivity of the diamond-Cu composite are discussed. The results demonstrate that the chromium element can improve the thermal conductivity of the composites and the thermal conductivity is largest when the content of chromium is 3 percent.

Abstract: Bulk nanostructured Al-4Cu alloy was synthesized by high energy ball milling followed by vacuum hot pressing. Its thermal stability was investigated up to 450°C using differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy. The results showed that grain growth in this Al-4Cu alloy was very limited and grain sizes in the range of 100 nm were still present in the alloys after exposure to 450 °C corresponding to a temperature as high as 0.77 T/Tm. The TEM investigations reveal that such a high thermal stability against grain growth observed in this alloy is attributed to the presence of ultrafine dispersoids.

Abstract: In the present study, Ti50Cu28Ni15Sn7 metallic glass and its composite powders reinforced with 4~12 vol% of SiC additions were successfully prepared by mechanical alloying. The as-milled Ti50Cu28Ni15Sn7 and composite powders were then consolidated by vacuum hot pressing into disc compacts with a 10 mm diameter and thickness of 2 mm. The structure of the as-milled powders and consolidated compacts was characterized by X-ray diffraction. While the thermal stability was examined by differential scanning calorimeter. In addition, the mechanical property of the consolidated bulk metallic glass and its composite was evaluated by Vickers microhardness tests. In the ball-milled composites, initial SiC particles were homogeneously dispersed in the Ti-based alloy glassy matrix. The presence of SiC particles did not dramatically change the thermal stability of Ti50Cu28Ni15Sn7 glassy powders. BMG composite with submicron SiC particles homogeneously embedded in a highly dense nanocrystalline/amorphous matrix was successfully prepared. A significant hardness increase with SiC additions was noticed for consolidated composite compacts.

Abstract: The preparation of Ti50Cu28Ni15Sn7 metallic glass composite powders was accomplished by the mechanical alloying of a pure Ti, Cu, Ni, Sn and carbon nanotube (CNT) powder mixture after 8 h milling. In the ball-milled composites, the initial CNT particles were dissolved in the Ti-based alloy glassy matrix. The thermal stability of the amorphous matrix is affected by the presence of the CNT particles. Changes in Tg and Tx suggest deviations in the chemical composition of the glassy matrix due to a partial dissolution of the CNT species in the amorphous phase. The bulk metallic glass composite was successfully prepared by vacuum hot pressing the as-milled CNT/ Ti50Cu28Ni15Sn7 metallic glass composite powders. A significant hardness increase with the CNT additions was observed for the consolidated composite compacts.

Abstract: Mg55Y15Cu30 metallic glass powders were prepared by the mechanical alloying of pure Mg, Y, and Cu after 10 h of milling. The thermal stability of these Mg55Y15Cu30 amorphous powders was investigated using the differential scanning calorimeter (DSC). Tg ,Tx , and Δ Tx are 442 K, 478 K, and 36 K, respectively. The as-milled Mg55Y15Cu30 powders were then consolidated by vacuum hot pressing into disk compacts with a diameter and thickness of 10 mm and 1 mm, respectively. This yielded bulk Mg55Y15Cu30 metallic glass with nanocrystalline precipitates homogeneously embedded in a highly dense glassy matrix. The pressure applied during consolidation can enhance thermal stability and prolong the existence of amorphous phase within Mg55Y15Cu30 powders.

Abstract: Fabrication of Fe3AlC matrix in-situ composite, reinforced by a FeAl phase, was studied by using the powder metallurgical processing route. Especially, in order to disperse the second phase more finely, we chose the mechanical alloying process. We investigated the microstructural and mechanical properties of the consolidated material. After consolidation by vacuum hot pressing, the compact showed almost full density and consisted of a Fe3AlC matrix and FeAl second phase (average particle size was less than 1μm). The compact showed HV746, which was higher than that of the arc melted Fe3AlC monolithic material, HV650.

Abstract: The preparation of Mg49Y15Cu36 metallic glass composite powders was accomplished by mechanical alloying of pure Mg, Y, Cu, and WC powder mixture after 10 h milling. In the ball-milled composites, initial WC particles were homogeneously dispersed in the Mg-based alloy glassy matrix. The metallic glass composites powders were found to exhibit a large supercooled liquid region before crystallization. Bulk metallic glass composites were formed by vacuum hot pressing the as-milled WC/ Mg49Y15Cu36 metallic glass composite powders at 473 K in the pressure range of 0.72-1.20 GPa. BMG composite with submicron WC particles homogeneously embedded in a highly dense nanocrystalline/amorphous matrix was successfully prepared under pressure of 1.20 GPa. It was found that the applied pressure during consolidation could enhance the thermal stability and promotes nanocrystallization of WC/ Mg49Y15Cu36 BMG composites.