Characterization of Ti-6Al-4V Bar for Aerospace Fastener Pin Axial Forging

Ti-6Al-4V warm forged fasteners are a critical part of the aerospace industry, as they are used in vast quantities for mechanical joining of components for the fuselage, wing-skin and aero-engine. These components are produced in vast quantities at rapid production rates through multi-blow axial forging However the rate that they are manufactured means that manufacturers rely upon periodic part conformance testing to understand if the part is within tolerance or if any undesirable manufacturing defects such as cracks or underfilling are present. Thus, a right-first-time manufacturing approach is essential to minimize non-conformant scrap. An analysis of the Ti-6Al-4V supplied raw material for axial forging, in a variety of different bar diameter sizes and from different industrial suppliers, was conducted. This was to attempt to understand whether material property variation or operator variation was the root cause for some material behaving differently during the manufacture route. Experimental testing was performed through microstructure characterization and mechanical testing methods. The volume fraction of the β-phase was noted to be marginally higher in material with good forgeability. The hardness of the inner core of the bar appears to be a critical material property for the Ti-6Al4V bar, with an overly hard bar-core hindering forgeability of the bar. This is believed to be due to the hotter central region malleability being key for forgeability. Micro-void porosity was also noted which could lead to stress concentration locations, or crack initiation, and as such is a deleterious property for forgeability. The experienced forgeability of the Ti-6Al-4V bars have been demonstrated to be sensitive to rather small variation in measured microstructure and mechanical property. It is believed that cumulative impacts of small differences, 1% variation in α-phase volume fraction, small variations in elongation to failure, 1% variation in elastic modulus and microhardness profile variation at the center of the bar of less than 10 HV0.3, can combine to significantly impact the forgeability of Ti-6Al-4V bar

High temperature electrical resistivity measurements of sintered samarium cobalt magnets

When modelling permanent magnet motors, it is important to understand the resistivity of the magnetic material, and its eddy current flow. These motors often operate over a wide range of temperatures and thus an understanding of the temperature dependency of resistivity is necessary for accurate modelling.For SmCo type magnets it has been shown that electrical resistivity can be anisotropic for 1:5 and 2:17-type magnets, and that operating temperature can significantly change resistivity.The authors investigated the temperature dependence of different commercial grade SmCo 2:17-type and 1:5-type magnets, up to 200 °C, in both a magnetised and non-magnetised condition. Anisotropic resistivity was observed in both types, with the 2:17-types having lower resistivity in the plane perpendicular to the c-axis, and the 1:5-type having lower resistivity in the parallel plane. At room temperature, resistivity was found to be similar in both the magnetised and non-magnetised states and a linear increase in resistivity was observed with increasing temperature for both. However, the temperature coefficient was found to be lower in the magnetised state, leading to a lower resistivity at higher temperatures than for the non-magnetised state.For 2:17-type magnets of similar composition, differences in the Zr content and the Zr-rich lamellae within the cellular structures were found to produce variations in the resistivity, only in the axis perpendicular to the c-axis. An additional 0.31 wt% of Zr is shown to lower resistivity by 0.7%

Evaluation of the thermal aging of δ-ferrite in austenitic stainless steel welds by electrochemical analysis

Abstract Cr-segregation by spinodal decomposition and G-phase precipitation were observed in δ-ferrite of austenitic stainless steel welds thermally aged at 400 °C for up to 20,000 h. A reversion heat treatment (R-HT) at 550 °C for 1 h dissolved the Cr-segregation in the aged welds while some intermetallic precipitates were present. The double-loop electrochemical potentiokinetic reactivation (DL-EPR) analysis showed no significant differences among them. However, after selective etching of the austenite phase, the DL-EPR values of δ-ferrite phase steadily increased with aging time due to the growth of Cr-depleted regions by spinodal decomposition. The electrochemical behavior of δ-ferrite after R-HT condition was similar to that of unaged welds, indicating the intermetallic precipitates did not affect the corrosion resistance in this case. Overall, DL-EPR analysis of δ-ferrite phase provided better correlation with spinodal decomposition