Canadian and French university teams have joined efforts in carrying out an experimental and theoretical study of the dissolution behavior of the hard-alpha inclusion in liquid titanium alloys. Synthetic hard-alpha dense particles of up to 6 wt pct nitrogen and nitrided sponge of up to 15 wt pct nitrogen were partially dissolved in a titanium or a titanium alloy bath. The metallographic examinations and microprobe analysis show that the dissolution process is always controlled by the outward diffusion of nitrogen into the bath through an external layer of beta phase. The growth of this beta phase layer depends on the velocity of liquid flow in the bath and can lead to an initial increase in the inclusion size. For porous particles, the diffusion of nitrogen from the pellet matrix to the infiltrations gradually leads to a partial densification of the inclusion. A numerical representation of the dissolution problem was developed, including the transient diffusion of nitrogen through intermediate solid phases. The comparison is good between the numerical simulations, the experimental measurements, and the dissolution kinetics given in the literature.
Purpose -Powder bed fusion additive manufacturing (PBFAM) of metal components has attracted much attention, but the inability to quickly and easily ensure quality has limited its industrial use. Since the technology is currently being investigated for critical engineered components and is largely considered unsuitable for high volume production, traditional statistical quality control methods cannot be readily applied. An alternative strategy for quality control is to monitor the build in real time with a variety of sensing methods and, when possible, to correct any defects as they occur. This article reviews the cause of common defects in powder bed additive manufacturing, briefly surveys process monitoring strategies in the literature, and summarizes recently-developed strategies to monitor part quality during the build process. Design/methodology/approach -Factors that affect part quality in powder bed additive manufacturing are categorized as those influenced by machine variables and those affected by other build attributes. Within each category, multiple process monitoring methods are presented. Findings -A multitude of factors contribute to the overall quality of a part built using PBFAM. Rather than limiting processing to a pre-defined build recipe and assuming complete repeatability, part quality will be ensured by monitoring the process as it occurs and, when possible, altering the process conditions or build plan in real-time. Recent work shows promise in this area and brings us closer to the goal of wide-spread adoption of additive manufacturing technology. Originality/value -This work serves to introduce and define the possible sources of defects and errors in metal-based PBFAM, and surveys sensing and control methods which have recently been investigated to increase overall part quality. Emphasis has been placed on novel developments in the field and their contribution to the understanding of the additive manufacturing process.
The major difficulty in applying high strain fatigue data to technological problems lies not in the fatigue aspect per se but in the prediction of the cyclic strain amplitudes. In this paper they are postulated for the cyclic bending of beams using large deflection theory and taking into account the changing stress-strain relationships which occur as cycling progresses. These theories have been tested using beams of rectangular cross section made of three different materials: mild steel, stainless steel, and an aluminum alloy. Good correlation has verified their applicability.
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