Juliano Soyama

Sintering behaviour of Ti–45Al–5Nb–0.2B–0.2C alloy modifications by additions of elemental titanium and aluminium

The sintering behaviour of a titanium aluminide alloy (Ti–45Al–5Nb–0.2B–0.2C in at.-%) with variations in the aluminium content was investigated. Additions of pure titanium to prealloyed powder of the starting composition were used to decrease the aluminium content to 43 and 44 at.-%, while additions of elemental aluminium increased it to 46 and 47 at.-%. Although the microstructures obtained were always fully lamellar, the porosity levels were different indicating a change in the sintering behaviour induced by the additions of elemental powders. Titanium additions lowered the optimum sintering temperatures, while aluminium additions shifted it to higher values. A reaction between the titanium aluminide prealloyed powder and pure aluminium was found to critically affect the sintering process.

Microstructural Features of Sn-3.0Ag-0.7Cu Alloy Prepared by Conventional and Microwave Sintering

In the present contribution, atomised Sn-3.0Ag-0.7Cu powder alloy with a size of less than 250 μm was first compacted and then microwave and conventionally sintered at 175 °C for 15 and 120 minutes, respectively. Despite the very different processing times applied, the degree of porosity was very similar, i.e., around 7%. The as-atomized microstructure of the conventionally sintered samples was barely altered with β-Sn dendritic matrix comprising Cu6Sn5 and Ag3Sn intermetallic particles. The microwave sintered Sn-3.0Ag-0.7Cu sample exhibited a combination of fine and very coarse intermetallic particles, with the presence of well-developed needle-like Ag3Sn, and its dendritic pattern disappeared completely. The Vickers hardness of both samples was measured and found to be consistent with their microstructures.

Influence of α-Phase Field Heat Treatment on the Tensile and Primary Creep Resistance of a Powder Metallurgical Processed Ti-45Al-5Nb-0.2B-0.2C Titanium Aluminide Alloy

In powder metallurgical processing the sintering process, as well as heat treatments, can drastically influence microstructure formation. In the case of γ-titanium aluminides, it is critical to achieve certain microstructure parameters, such as colony size, porosity and grain boundary morphology in order to obtain appropriate mechanical properties. In this study, the effect of a heat treatment implemented after sintering with the objective of varying the colony size was investigated. Specimens of Ti-45Al-5Nb-0.2B-0.2C prepared by metal injection moulding and uniaxial pressing of feedstock were used to evaluate the tensile and creep properties. Heat treatments conducted at 1350 and 1400 °C for 3 h led to colony sizes of approximately 100 and 200 μm, respectively. Classically, there is an inverse relationship between grain size and creep resistance, nonetheless, for γ-titanium aluminides, the morphology of the colony boundaries was also found to play a role. The larger colony sizes achieved with the heat treatments did not improve the primary creep resistance, which was explained by the change in the morphology of the colony boundaries as they became larger.

Axial fatigue testing of Ti–6Al–4V using an alternative specimen geometry fabricated by metal injection moulding

The hourglass-shaped specimen, which is commonly used for axial fatigue testing, cannot be easily fabricated by metal injection moulding. Consequently, this work aimed at evaluating the performance of an alternative specimen (dog bone geometry) for fatigue characterisation. Additionally, an effort towards the assessment of the fatigue damage with specimens fatigued until halflife was made. The alloy used in this study, serving as an example for the test validation, was Ti–6Al–4V. The feasibility of using the specimens for fatigue testing was confirmed with a narrow scatterband, however, only in the range of 105 cycles. The crack initiation sites were always found on the surface associated with quasi cleavage facets. Specimens fatigued until halflife showed a decrease in ductility in conventional tensile testing; nonetheless, the ultimate tensile strength remained unchanged.