Papers by Keyword: Direct Powder Rolling

Abstract: Direct powder rolling (DPR)/roll compaction has been labelled a complex and sample sensitive process. As such the design of the instrument and the determination of the optimal processing conditions for a given feed are very challenging. The challenge is attributed to a wide range of operating parameters and material properties. Several theoretical models can be used to evaluate the interaction of the different parameters and properties and how their changes affect the rolling process. In this study, the Johanson theory was used to determine the rolling parameters of titanium powder. Preliminary results of the nip angle, nip pressures and maximum horizontal pressures of the mill for the powder rolled on a 55mm diameter roll with roll gap sizes of 0.175, 0.15 and 0.05 mm were obtained. The results were found to be acceptable for the nip angle estimation, however improvement on predicting the maximum horizontal pressure is required.

Abstract: In this study, direct powder rolling was applied to make thin sheets from HDH (hydrogenation and dehydrogenation) powders. Effects of materials and process parameters on tensile properties of sintered sheets are investigated. In the direct powder rolling with two-horizontal counter-rotating rollers, materials parameters including powder size and process parameters such as roll gap, roll speed, and packing height are controlled. With -100mesh Ti powders, CP titanium sheets of a thickness up to 1.5mm and a width up to 300mm were obtained without any rolling defects. Sintering of the rolled strips was performed between 1000°C and 1250°C at 50°C intervals for 1hour to 4 hours. The relative density of the sintered strips was found to be around 85 to 90 percent. After sintering, the complete densification was made by cold rolling, and microstructures and tensile properties were evaluated after annealing treatment at 750°C for 2 hours.

Abstract: A significant research effort within the CSIRO Light Metal Flagship is aimed at developing new processes for the manufacture of (semi-finished) titanium products based on a powder metallurgy approach. The main driver for considering alternative processing and consolidation techniques to conventional ingot metallurgy is improved techno-economics associated with a reduction in processing steps and increased productivity via rapid consolidation of parts. In this respect, CSIRO has developed a process to manufacture sheet products utilising direct powder rolling; the process consists of cold rolling the powder feedstock to a green strip, which is then rapidly heated and hot rolled to consolidate the material completely. The work reported here was an investigation into the feasibility of fabricating Ti-6Al-4V strip by a blended elemental powder metallurgy route. The development of microstructures occurring during the processing and heat treatment steps has been studied. The generic roles of some process, material and heat treatment variables on the tensile properties and homogeneity of the final material have been assessed and are discussed in this paper.

Abstract: The reaction mechanism of silicon and iron composite powders was clarified during the fabrication of high silicon iron sheet with the Si-content of 6.5wt% by Direct Powder Rolling (DPR) technique. The changes of phase composition and structure evolvement were mainly studied. It is found that a local graded structure, Fe-Fe(Si)-Fe3Si(Si)-Si, forms when sintering at 950-1000oC, which plays an important role in the DPR process. Fe3Si(Si) phase keeps higher content of Si, and Fe(Si) phase remains the state with much lower Si-content, thus provides good mechanical proprieties of rolling and cutting. Then, the subsequent sintering at about 1200oC improves the density and makes the distribution of Si homogeneous in the final high silicon iron sheets.

Abstract: The changes of phase composition and structure evolvement of Fe and Si powders with the ratio of 6.5wt%Si to 93.5wt%Fe were mainly studied. It is found that, the local graded structure, Fe-Fe(Si)-Fe3Si-(FeSi)-Si, forms due to the obvious diffusion and the alloying reaction between Fe and Si powders when sintering at 900-975oC. The graded structure, in which the high silicon phase based on Fe-Si alloys is packed by the low silicon solution based on Fe, exhibits a graded concentration of Si distribution. And most of the Fe-containing phase remains a state of lower Si content, less than that of 3wt%Si-Fe alloy, thus provides the good deformation behavior of rolling and cutting for the compacts. Therefore, it is feasible for the high silicon iron sheets to be produced by the powder metallurgy method.