Materials Science Forum Vols. 534-536

Abstract: The continuously porous t-ZrO2 bodies were fabricated by the extrusion process. The average pore size of the 2nd passed samples was about 260μm in diameter. The maximum bending strength value was about 177MPa. For the evaluation of their biocompatibility, human osteoblast like MG-63 cells and osteoclast like Raw 264.7 cells were cultured on the top surface of the porous t-ZrO2 bodies. The osteoblast cells were grown with spindle shape, condensed circular growth and three-dimensional network type. In contrast, the osteoclast cells appeared with pebble stone structure.

Abstract: In this study, rod type Cu54Ni6Zr22Ti18 bulk amorphous alloy fabricated by warm extrusion of amorphous powders was investigated. To get bulk type amorphous alloy, the Cu54Ni6Zr22Ti18 amorphous powders which has a particle size below 63( and wide supercooled liquid region of 53K were prepared by a high-pressure gas atomization method. The powders were filled in a Cu can with an inner dimension 20×2×50mm in air, evacuated, sealed and then precompacted in the press. Before extrusion, the billet was heated with heating rate of 50K/min and the holding time was about 5min. The extrusion temperature was 723K and the extrusion ratio was increased from 2 to 5. By warm extrusion of amorphous powders, a fully amorphous Cu54Ni6Zr22Ti18 bulk type alloys were successfully synthesized. The conditions for extrusion were decided based on the time-temperature-transformation curve and DSC analysis. Phase analysis was performed by XRD. The result of the phase analysis indicated that Cu54Ni6Zr22Ti18 bulk rod type samples having fully amorphous phase could be obtained until extrusion ratio of 4 at extrusion temperature of 723K, but partial crystalline phase would be observed in the bulk rod type alloy fabricated at extrusion ratio of 5.

Abstract: High-Speed Centrifugal Compaction Process (HCP) is a wet compacting method, in which powders are compacted under a huge centrifugal force. The HCP was well applied to small alumina specimens, but the compact easily cracked when we applied the HCP to other materials. In the present study we clarify the mechanism that introduces such cracks. Firstly, we observed HCP alumina, dyeing with iron oxide powder or by the Immersion Liquid Technique, and found that there was a kind of flow pattern generated during the HCP. A simple simulation also revealed that the formation of such a flow pattern was related to the Colioli’s force in the centrifugal field, and therefore was hard to suppress. Nonetheless, the actual introduction of inhomogeneity along the flow was largely affected by another factor. Die releasing oil was dragged in the flows and formed low density regions along the flow.

Abstract: High velocity compaction (HVC) is a production technique with capacity to significantly improve the mechanical properties of powder metallurgy (PM) parts. Several investigations indicate that high-density components can by obtained using HVC. Other characteristics are low ejection force and uniform density. Investigated here are green body data such as density, tensile strength, radial springback, ejection force and surface flatness. Comparisons are performed with conventional compaction using the same pressing conditions. Cylindrical samples of a pre-alloyed water atomized iron powder are used in this experimental investigation. The different behaviour of HVC-pressed green bodies compared to conventional pressed green bodies are analysed and discussed. The HVC process in this study resulted in a better compressibility curve and lower ejection force compared to conventional quasi static pressing. Vertical scanning interferometry (VSI) measurements show that the HVC process gives flatter sample surfaces.

Abstract: Since 2000, CETIM has been equipped with a High Velocity Press that can deliver up to 5 shots per second with each blow accurately set up (up to 20000J) thanks to the impact velocity regulation (up to 11m.s-1). Through different projects, CETIM and its scientific and industrial partners have evaluated the potential of this new technology in terms of materials and component shape. Various kinds of powder materials were studied: metals, ceramics and polymers. The HVC process was used with success to manufacture gears, large parts and multilevel components. More than, the green machining process that enables shapes to be produced that would otherwise be impossible to compact is improved by the high density of HVC parts and it is also an opportunity to produce components with very hard sintered materials.

Abstract: In the present work, two kinds of steel powder were (Distaloy HP-1 & Ultrapac-LA) selected and subjected to powder metallurgy processing. For Ultrapac-LA, a heterogeneous microstructure consisting of tempered martensite, nickel-rich ferrite, divorced pearlite and nickelrich regions surrounding pores was observed. For Distaloy HP-1 in slow cooling rates (0.4 °C.s-1), the amounts of martensite and bainite varied between 50-60% and 30-40%. However, for fast cooling rates (1.2 °C.s-1), the variation was between 70-80% and 10-20%. The mechanical properties of the prepared samples were studied with controlled production conditions such as cooling rate and heat treatment. The increasing porosity was found to play an important role in the tensile stress and fatigue strength. The ultimate tensile strength and fatigue strength were more than 1000 MPa and 400 MPa in this research (for Distaloy HP-1, 7.2 g.cm-3, 0.5% carbon content and fast cooling rates). Macroscopic examination of the fracture surfaces for all specimens revealed that fatigue crack growth and final fracture regions were brittle and without noticeable permanent deformation. The final fracture regions for all tests were very similar, and the final fracture in these two material conditions revealed brittle macrobehavior and ductile microbehavior.

Abstract: During cold compaction processes loose powder is pressed under tooling action in order to produce complex shaped engineering components. Here, the analysis of the plastic deformation of granular packings is of fundamental importance to the development of computer simulation models for industrial forming processes. Powders can be idealized by packing discrete particles, where each particle is a sphere meshed with finite elements. During pressing, particles are deformed by elastic-plastic hardening where friction is present at each contact. The pressing of an isolated particle followed by a body centered cubic packing was compared with numerical prediction and experimental data. The analysis was focused on the interaction between particles and the global response expressed in force-displacement curve during compaction. The accuracy of the numerical models was also analyzed for high relative densities up to 0.95.

Abstract: The results of monotonic and cyclic uniaxial compression tests, in which the deviatoric component of the stress is predominant, carried out on green and recrystallized iron compacts with different levels of density are presented and discussed in order to analyse the macro and micromechanisms governing the mechanical behaviour of non-sintered PM materials. The plastic deformation of the particles, especially at the contact areas between neighbouring particles, produces an internal friction responsible for the main features observed in the behaviour of green metallic compacts. These experimental results show important discrepancies with the plasticity models, Cam-Clay and Drucker-Prager Cap, used to simulate the powder compaction stage. Possible causes for these discrepancies are pointed out.

Abstract: Organically bonded P/M mixes have been developed to improve the stability of dimensional properties by reducing the segregation of the mix constituents and improving the filling characteristics. Robustness and reliability are key factors for the promotion of P/M as cost effective substitute of competing manufacturing technologies. Based on the production of four different belt pulleys, this paper presents the achievement of reduced weight scatter and close dimensional control realizable by using a StarmixTM that is organically bonded.

Abstract: Powder mixes used in the P/M industry contain ingredients of substantially different particle sizes and specific gravities that have a strong tendency to segregate during handling. Reducing or eliminating this segregation is essential for the part producer to achieve consistent precision and optimum performance. Treating the premixes with polymer binders helped to resolve this problem. Binder/lubricant systems have been developed that provide improved flow rates combined with increased green densities and green strengths. A review of these developments will be presented and their impact on overall productivity and performance will be outlined.