An Evaluation of the Mechanical Behavior of Bronze-NI Composites Produced by Selective Laser Sintering

Mechanical properties of Bronze-Nickel composites produced by Selective Laser Sintering (SLS) were evaluated by constant displacement tension tests. These were studied as a function of SLS process parameters - laser power density, scan speed, scan spacing, scan direction and layer thickness. The strength data was then correlated to the microstructure and the part bulk density. To further enhance the part densities and the mechanical properties, post-SLS sintering was studied. The relationships between SLS process parameters, post-SLS sintering parameters and the resulting microstructures, part bulk density and the mechanical properties will be described.Mechanical Engineerin

Densification of Selective Laser Sintered Metal Part by Hot Isostatic Pressing

Metal matrix alloy composite parts were made from powders by Selective Laser Sintering (SLS). In this study, partially dense (60%-80%) metal parts made by SLS were densified to full density (>98%) by hot isostatic pressing (HIPping) without any loss of shape. HIPping was done by vacuum sealing SLS samples in glass capsules. HIPping parameters, such as, temperature, pressure, and time, were studied with respect to density, linear shrinkage, and microstructures. Anisotropy in linear shrinkage was correlated to the SLS processing parameters. Densification resulting from HIPping was correlated to microstructures and theoretical HIP densification maps. A detailed analysis of such maps is presented.Mechanical Engineerin

Gelcast Molding with Rapid Prototyped Fugitive Molds

A technique for the rapid manufacture ofceramic components has been developed using rapid prototyping to generate molds for the required components. The process entails the fabrication offugitive tooling using rapid prototyping techniques from which ceramic articles are formed using gelcasting. In the gelcasting process, the mold cavities are filled with a fluid suspension of ceramic powder which sets to a solid form through the polymerization of gelling additives and application of heat. The mold is carefully removed by dissolution or heat treatment leaving the intact gelcast part. The "green" gelcast part is subsequently dried and sintered to full density. Computer aided manufacturing of the tooling using solid freeform fabrication techniques allows for complex shapes to be manufactured with minimal tooling cost. The technique is idealfor the manufacture of ceramic parts in small batch conditions or for prototyping of functional parts in design cycles. Cost and time reduction of a magnitude can be achieved.Mechanical Engineerin

Synthesis, Selective Laser Sintering and Infiltration of High Super Tc Dual Phase Ag-YBa2Cu307-x Superconductor Composites

Fine, homogeneous dual phase Ag-YBa2Cu307-x composite powders were prepared by a simple colloidal sol-gel co-precipitation technique. Silver did not react with or degrade YBa2Cu307-x. Bulk porous samples of pure YBa2Cu307-x and Ag-YBa2Cu307-x were made from powders by Selective Laser Sintering. The porous parts were further densified by infiltrating silver into pores, resulting in a dense, structurally sound dual phase superconducting composite. Laser processing parameters were varied to obtain optimum microstructure. The laser sintered parts required oxygen annealing after infiltration to restore the orthorhombic, superconducting structure. X-ray diffraction and Tc measurements indicate some impurity phases present in samples processed under aggressive laser conditions.Mechanical Engineerin

Oxygen-enrichment of YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-&#948;</SUB> using the fluidization technique

The oxygen-deficient phase of the high Tc superconductor, YBa2Cu3O7, was oxygen-enriched using the fluidization technique to give good superconducting properties. The normal method of oxygen treatment at 900&#176;C for 24 h and at 600&#176;C for 24 h has been reduced to just one treatment at 600&#176;C for 12 h by the fluidization technique to achieve almost the same strength of superconducting signal for the YBa2Cu3O7 powder, which establishes the attractiveness of the latter route for the large-scale preparation of superconducting material. The particle sizes were in the range 0-90, 90-180 and 180-420 &#956;m. The fluidized particles were crystalline with orthorhombic distortion. Tconset, estimated using the a.c. magnetic susceptibility method, was 91&#183;3 K. The volume fraction of superconducting material in the product was 83&#183;7-85&#183;3%, one of the highest values reported so far for YBa2Cu3O7