Yannig Thomas

Interstitial elements in titanium powder metallurgy: sources and control

Abstract The effect of interstitials on the mechanical properties of cast and wrought titanium alloys has been extensively reported but less information is available on the effect of contamination during PM processing. The sources of interstitial contamination when processing titanium powders by compaction, isostatic pressing, powder injection moulding (PIM) and innovative foaming processes are reviewed, focusing specifically on oxygen. The initial powder characteristics (surface area, size), process parameters (time, temperature) and environment (atmosphere, binder, support) may all have significant impact on the final interstitial content. It is, therefore, important to identify and control the sources of contamination by interstitials. A case study on PIM is provided to illustrate the relative contribution of the different sources.

Production of Metallic Foams Having Open Porosity Using a Powder Metallurgy Approach

Abstract A technique has been recently developed to produce foamed metallic structures from dry powder blends containing a metallic powder, a polymeric binder, and a foaming agent. The blend is molded and heat-treated to foam and consolidate the material. The final properties may be tailored by varying the sintering temperature. Microstructure, chemical composition, and properties of nickel (Ni) foams sintered at different temperature are presented and discussed. The resulting material has an open cell microstructure with three levels of porosity. This structure leads to materials having low density (∼ 90% porosity) and high specific surface area. The specific surface area is reduced and the mechanical strength is increased when the sintering temperature increases.

Partially Water-Soluble Binder Formulation for Injection Molding Submicrometer Zirconia

A binder system containing 60% by volume of a water-soluble major constituent was formulated and tested for powder injection molding ceramic materials. The main components of the binder phase were a low molecular weight polyethylene glycol, an oxidized high density polyethylene, polyvinyl butyral and stearic acid. Ceramic powder-binder mixes containing these binder components and up to 45% by volume of a submicrometer stabilized zirconia powder were prepared and characterized. The apparent viscosity of these mixes at a temperature of 190°C and a shear rate of 100 s-1 was determined to be 700–800 Pa·s. Binder removal from parts produced by injection molding these feedstocks was accomplished using a two-stage process. The water-soluble constituent, polyethylene glycol, was removed by dissolution in water at 50°C. Tests showed that approximately 90% of the polyethylene glycol could be removed from a 2-mm thick part during a 2 h immersion in water. The remaining binder constituents were removed using a thermal treatment to 500°C at a heating rate of 100°C/h. Thermogravimetric analysis revealed a good separation of the decomposition regions for the various components when heated in an argon atmosphere. A final sintering step in air at 1500°C produced parts having a density above 99%.

In-Line NIR Monitoring of Composition and Bubble Formation in Polystyrene/Blowing Agent Mixtures:

The composition of mixtures of polystyrene (PS) and blowing agent (HCFC 142b) was monitored by means of near infrared (NIR) transmission probes located in the die at the end of an intermeshing co-rotating twin-screw extruder. The PS resin was extruded while the HCFC was injected at high pressure and various concentrations. Using chemometrics techniques like PLS to model the differences in the NIR spectra, the composition of PS/HCFC mixtures could be predicted accurately with a standard error of prediction (SEP) below 0.2 wt%. Accurate composition prediction was still possible in the presence of a small amount (<5% wt) of nucleating agent like talc. In-line NIR spectroscopy was also an effective technique to detect bubble formation in the die as a function of HCFC concentration and pressure.

Foam-coated MIM gives new edge to titanium implants

Titaniums characteristics of lightness combined with strength and compatibility with human tissue makes it an ideal metal for medical implants. When manufactured in porous forms, bone integration is encouraged giving long-term stability. Researchers in Canada have been looking at dental implants that have a dense titanium core and a porous foam composite coat…

Sintered Lamellar Soft Magnetic Composites: Shaping and Magnetic Properties

Sintered lamellar soft magnetic composite (SL-SMC) is a promising material for power frequency applications and for all types of electric motors, including induction motors. Alumina coated Fe-3%Si particles cut from steel sheets offer both the advantages of standard laminated steel products, and of soft magnetic composites (SMC). As SMC’s, this material can be shaped using standard near-net shape powder metallurgy (P/M) techniques, which represents a big advantage over coated laminated steel assemblies. Indeed, the P/M process, as compared to laminated steel assemblies, gives access to better design and improved motor assembling techniques, at lower production costs, by limiting machining and stamping. The unique structure of the SL-SMC offers better DC magnetic properties than standard SMC’s, allowing them to cover a larger range of applications. However, there still remains work to be done in developing this new technology to its full potential, using low cost industrial techniques. This paper is divided into two main parts. The first is dedicated towards assessing the possibility of producing SL-SMC parts using an automatic industrial compaction press. The impact of two different lubrication systems, admixed solid lubricants and die wall lubrication, on the density and green strength of the motor parts, will be determined. Also, the process capability will be evaluated on the basis of “part to part” stability. The second section of this study will determine the impact of different processing parameters on the mechanical and magnetic properties of the Fe-3%Si alloy. Results show that by carefully controlling heat treatment, very high maximum induction, low magnetic loss and good mechanical property, can all be reached in fabricated parts.