Papers by Author: César Edil da Costa

Abstract: Aluminum alloys have been increasingly applied as a structural material in composite materials using metal matrix due to their excellent mechanical properties and low weight. The reinforcement are of fundamental importance in composite materials, owing to the their responsibility to support stresses acting on the metal matrix. Therefore, ceramic reinforcements can be replaced by intermetallic components with high mechanical properties and good thermal stability. The intermetallic components react chemically with the matrix, characterized by strong interactions, which makes possible the development of the new families of materials. The composite materials using aluminum reinforced with nickel aluminides and ceramic were developed using techniques based on a combination of powder metallurgy and extrusion processes, which makes possible to obtain more dense materials under lower processing temperatures. The powders of AA6061 and Ni3Al were manually mixed for 30 minutes, with different percentages of intermetallics and ceramics particles, 5 and 10% in weight. The composite powders were submitted to a hot extrusion process for 40 minutes at 540oC, and 385 MPa, with a reduction ratio of 25:1. This process insures extruded composites with a refined structure and a good distribution of the reinforcement particles. The material characterization were performed through structural analysis via scanning electron microscopy; mechanical behavior via tensile and hardening tests; and analysis of the fracture. The results show that the method used is effective to obtain composite materials with improved characteristics.

Abstract: This work is concerned with issues related to using grey cast iron swarf from dry machining in powder metallurgy. In a first stage, a complete study on the characteristics of the raw powder is performed, in which aspects related to the dilution in different proportion of pure iron were studied. Low compacting pressure produces workpieces more resistant and that the ideal sintering temperature is 1160 °C. In a second stage, aiming at reduction of the powder, a heat treatment is performed. New dilutions using the decarburized powder were made and results showed better structural homogeneity and an improvement in the mechanical properties. The steel alloy 50/50% of swarf powder provided the best results. In a third stage, a cylindrical bearing was produced. New dilutions were made. Based on the control of the interconnected porosity, radial and wear resistance, the sample prepared with 100% swarf powder provided the best results.

Abstract: Hardmetal is usually processed by the conventional powder technology techniques: mix of WC + Co powders compacted and liquid phase sintering. A new method to process hardmetal parts is hereby described. Parts of WC-15%wt Co were processed by using high pressure – high temperature sintering. It was used the pressure of 5GPa, temperatures of 780-1200-1350-1400oC, and times of 2-4 minutes of sintering. Results are shown as a function of micro-structural evolution, densification, and hardness measurements.