Materials Science Forum Vols. 591-593

Abstract: Binders based on mixtures of polymers and waxes are suitable both for solvent combined with thermal extraction, as well as for pure thermal debinding. The recently developed plasma-assisted debinding and sintering (PADS) process has been targeted, for historical reasons, on a wax-polymer system, appropriated for solvent combined with thermal extraction processes. This paper shows experimental results related to the debinding rate of parts produced by metal powder injection molding using the recently developed Plasma Assisted Debinding process. Influence of temperature and the ratio of cathodic area on the mass loss were studied.

Abstract: Protetive atmospheres are used in powder metallurgy to prevent oxidation and to reduce oxides, to control carbon contents of iron and iron alloys, and to flush volatilized lubrificants from the furnace. Another important function of the atmosphere during sintering is to burn and remove the hydrocarbon lubrificants used to compact the powdered metal. However, one of the most important services that the Air Products "industrial gas company" can provide to its heat treat customers is assistance in troubleshooting their furnace(s) when there are problems. To be able to troubleshoot a furnace, it is important to know what the typical problems are that arise, what causes them and how to fix or minimize to problem. This work should aid in finding the source of the problem with analysis equipment, and, by using your knowledge of the furnace and the process, solve the problem. Summarizing, (1) ensure system integrity, (2) Know the required safety interlocks, and (3) Verify their operation.

Abstract: This work deals with the use of Fe-Cu alloys for use as matrix for diamonds in cutting tools. In this case it was processed diamond beads for diamond wires - used in the slabbing of dimension stones. Normally, diamond beads are PM processed. The beads of the present work were manufactured using Fe-Cu alloy with addition of 1wt% of SiC as the matrix metallic bond. It was carried out shrinkage/swelling and microstructural analyses, Brinell hardness measurements, as well as the abrasion resistance of beads produced here in confront with commercial ones. The results indicate that it was processed beads with similar abrasion resistance and performance than those of the commercial diamond beads.

Abstract: In this work, a study to process and characterize Fe-Cu alloys with reduced Co content is shown. The Fe-Cu-Co alloys were processed by elemental blending of powders of the system Fe- 15%wtCu with various amounts of Co, pressing at 350MPa, and sintering at 1150°C/25min./10-2 mbar. The sintered microstructure was observed. It was conducted hardness and wear tests, aiming to define the ideal Cu addition for future use in impregnated diamond tools. It was observed that higher Co contents results in improved hardness and wear resistance in the studied Fe-Cu alloys.

Abstract: A PADS (Plasma Assisted Debinding and Sintering) reactor developed by Lupatech S.A. has been employed to MIM process two Ni-based superalloys under Argon, at temperatures in the 1280 -1310 °C range, and for 2 to 3 hours. Both materials have chemical compositions similar to that of standard Nimonic® 90 but differ considerably in their powder characteristics. One type of powder was gas-atomized whereas the other was water-atomized. Samples of both materials in as-sintered states as well as subject to different HIP and heat treating conditions have been characterized mechanically in tensile tests and by HV measurements. The best overall results are attained by the water-atomized material sintered at lower temperatures. The PADS processing of these superalloys shows marked advantages over more conventional PM processing technologies. These results are particularly relevant to the development of turbine components for the automotive and aerospace industries.

Abstract: This paper discusses the preparation of partially amorphous Al90Fe5Cr5 and Al90Fe7Cr3 powder alloys by mechanical milling and their subsequent consolidation by hot milling. Samples milled for 60 hours showed a microstructure composed of amorphous phase and nanocrystalline Al. The heat treatment of these powders resulted in the equilibrium phases: fcc-Al + (Al3Fe and Al5Cr intermetallic phases). Hot rolling these powders at 430°C resulted in consolidated samples with a fine microstructure composed of Al, Al3Fe and Al5Cr intermetallic phases and high porosity. The high hardness values of about 417HV of the intermetallic compounds formed during the rolling process presented the main obstacle to obtaining totally homogenous and consolidated samples.

Abstract: Borides, especially transition metal borides, like Mo2FeB2 ternary boride, are promising candidates for wear resistance applications. However, poor sinterability and extreme brittleness raise difficulties to manufacture a structural material. In this work, the viability to obtain Fe-Mo-B alloys with high wear resistance materials obtained by PM techniques is studied. Other researchers use Cr and Ni alloyed steels and the B amount addition is very low. The main objectives are to increase the amount of B, not to use Cr alloyed steels and to decrease the sintering temperature. This can be obtained using mechanically alloyed Fe/B (50% by wt.) powders, which are highly reactive after milling for 36 h. The mixture has a composition of 40%Mo-40%Fe-20%Fe/B, being characterized by flow rate and apparent density. These materials were uniaxially compacted and vacuum sintered. Specimens were analysed by SEM and physical and mechanical properties were evaluated (density, dimensional change, bending strength, hardness and wear).

Abstract: In this work, ultrahigh carbon steels (UHCS) obtained by powder metallurgy with CIP and argon sintered at 1150°C. Then, they were rolled at 850 °C with a reduction of 40 %. Finally, steels were quenched at 850 and 1000 °C in oil. In each step, hardness, bending strength and wear performance were evaluated. Obtained results are justified with a metallographic study by SEM. Both mechanical properties and wear resistance are highly favoured with the thermomechanical treatment that removes the porosity of the material. Moreover, final quenching highly hardens the material. The obtained material could be used as matrix for tool steels.

Abstract: The deposition of pure tin onto pure aluminum powder in its self-convective motion by magnetron DC sputtering was examined in order to prepare Al-Sn composite powder and thereby to improve the sintering of the aluminum particles, aiming at the development of highly structure-controlled porous aluminum materials. The fabrication of porous aluminum materials was carried out by space-holder method using the prepared Al-Sn composite powder in ordinary powder metallurgy processing. The effects of the sputterdeposition of tin on porous structure and mechanical properties of the sintered compact were investigated. It was found that the porous structure of the sintered porous materials with the porosity 80% was better regulated by the sputter-deposition, compared to that without the deposition. Regarding their compressive properties, it was found that the plateau stress of the sintered porous materials reached by the sputter-deposition twice as high as that without the deposition. Therefore it was concluded that coating of aluminum powder with tin deposits enables the porous-structure to be controlled more effectively in fabricating sintered highly porous aluminum materials, as well as improves their mechanical property.

Abstract: Cr3C2-NiCr coatings have been used for corrosion and wear resistant applications. In the last decade, thermal sprayed coatings using nanostructured feed stock of other materials has exhibited higher hardness, strength and corrosion resistance. Hence, it is anticipated that nanostructured Cr3C2-NiCr coatings will also exhibit these properties and therefore posses improved performance characteristics. Preparation of nanostructured feed stock powders is the first step in the synthesis of nanostructured coatings and mechanical milling is an effective process to obtain the powders. Preliminary studies in which commercial Cr3C2-NiCr powders were milled in hexane and gaseous nitrogen revealed that particle and crystallite size were significantly smaller in powders milled in nitrogen. This paper presents the effect of hexane content and milling parameters on Cr3C2-Ni20Cr powder characteristics. Use of just sufficient hexane as the milling media reduced significantly the particle and crystallite sizes.