Measuring Threshold Pressure of Melt Magnesium Infiltrating into Al2O3sf Porous Preform with Fast Method

Threshold pressure is a very important parameter for melt alloy successfully infiltrating into the porous preform. However, the precise measurement for threshold pressure is very difficult for the reason that infiltration process is undertaken very fast under extreme elevated temperature and high pressure without effective measuring devices to monitor it. A totally new measuring device was proposed and fabricated, which can be used to monitor the infiltration process “visually” and measure the threshold pressure directly at the same time. The infiltration speed can be controlled by adjusting the gas flow speed. The infiltration behavior of melt AZ91D alloy in Al2O3sf preform was researched at temperature of 800°C and pressure of 0.6 MPa. The optimized gas velocity was controlled at 25L/min. The degree of vacuum of the infiltration cavity was set 30kPa in experiments. The volume fraction of Al2O3sf was 10%. Under these conditions, the threshold pressure of melt AZ91D alloy into porous Al2O3sf preform was found to be related with vacuum degree in infiltration chamber, and it was about 30 kPa

Properties of B4C-Based Composite with Layered Structure

A three-layer material based on B4C/Al, B4C/TiB2 and B4C composites had been successfully prepared. The microstructures and properties of B4C/Al-B4C/TiB2-B4C composite were investigated in detail. The three-layer porous preform was first prepared by hot pressing. Then the three-layer composite was fabricated by infiltrating aluminum into the porous preform in vacuum. The three-layer B4C/Al-B4C/TiB2-B4C composite showed good interfacial bonding. When using the B4C ceramics layer as the load-bearing surface, the flexural strength, fracture toughness and Vickers hardness of the composite were 230 MPa, 3.4 MPa·m1/2 and 38 GPa, respectively.

Fabrication of Carbon Nano-Fiber / Aluminum Composites by Low-Pressure Infiltration Method

In this study, the fabrication of carbon containing aluminum composites was attempted by using low-pressure infiltration method. At first, porous preform containing vapor grown nano-fiber (VGCF) and pure aluminum powder was fabricated by spark plasma sintering (SPS) method. Porosity in preform was controlled by changing the applied pressure during plasma sintering. Consequently, the porous preform with 40-50vol％ in porosity was obtained, which has enough compression strength for low-pressure infiltration (<1MPa). Then, the molten pure aluminum infiltrated to porous preform with 0.4MPa in applied pressure at 1023K, and consequently we can obtain the composite with 62-86% in density. The electrical and thermal conductivity of composites was affected by the porosity, strongly.

Numerical Analysis of Powder Forging Under Various Initial Density Distributions and Friction Conditions

Finite element models have been developed to simulate forging of sintered porous powder metal. The deformation behaviour of the porous preform during hot forging has been described by the Duva and Crow porous material constitutive model. It has been implemented into general purpose nonlinear finite element software within a large deformation formulation. Most of the previous finite element analyses of the deformation of this porous preform always assume an initial homogeneous density distribution within the compacted porous preform. However, the compacted parts obtained after compaction and sintering usually possess inhomogeneous density distribution. The present finite element models therefore take into account the initial distribution of relative density within the preform. The simulations have been conducted for various initial density distributions and under various frictional conditions in order to investigate the deformation characteristics and the evolution of voids in the forging process.