Effect of stress relieving heat treatment on surface topography and dimensional accuracy of incrementally formed grade 1 titanium sheet parts

The forming of parts with an optimized surface roughness and high dimensional accuracy is important in many applications of incremental sheet forming (ISF). To realize this, the effect of stress relieving heat treatment of grade-1 Ti parts performed before and after forming on the surface finish and dimensional accuracy was studied. It was found that heat treatment at a temperature of 540 °C for 2 h improves the surface finish of formed parts resulting in a surface with little or no visible tool marks. Additionally, it improves the dimensional accuracy of parts after unclamping from the rig used for forming, in particular, that of parts with shallow wall angles (typically <25°). It was also noted that post-forming heat treatment improves the surface finish of parts. The surface topography of formed parts was studied using interferometry to yield areal surface roughness parameters and subsequently using secondary electron imaging. Back-scatter electron microscopy imaging results coupled with energy-dispersive X-ray (EDX) analysis showed that heat treatment prior to forming leads to tool wear as indicated by the presence of Fe in samples. Furthermore, post-forming heat treatment prevents curling up of formed parts due to compressive stresses if the formed part is trimmed

High temperature deformation behavior of Ti-6Al-4V alloy with Widmanstaten microstructure

A series of load-relaxation tests were, conducted on Ti-6Al-4V alloy with a transformed microstructure to investigate high temperature deformation mechanisms. The. flow stress-vs.-strain rate curves were well fit with the inelastic deformation equation describing grain matrix deformation (dislocation glide + dislocation climb). However, for the heavily deformed (epsilon approximate to 1.2) specimens, the operation of grain-boundary sliding as well as the grain matrix deformation was evidenced. The grain boundary sliding rate was found to be most rapid for the microstructure with the thinnest alpha laths/platelets.X111sciescopu

Deformation behavior of Ti-6Al-4V and Ti-6.85Al-1.6V alloy with a globular microstructure

The high temperature deformation mechanisms of two phase alpha+beta alloy and a near-alpha alloy were investigated, and compared within the framework of inelastic-deformation theory. For this purpose, load-relaxation tests were conducted on the two alloys at temperatures of 750 similar to 900 degrees C. The flow stress-vs.-strain rate curves for both alloys were well fit with inelastic deformation equations describing dislocation glide and grain boundary sliding. The amount of grain boundary sliding resistance was higher in the near-cc alloy rather than the two phase alpha+beta alloy due to difficulty in stress relaxation at triple junction region.X11sciescopu

Constitutive analysis of the high-temperature deformation of Ti-6Al-4V with a transformed microstructure

The high-temperature deformation mechanisms of Ti-6Al-4V with a transformed microstructure were determined within the framework of inelastic-deformation theory. For this purpose, load-relaxation tests were conducted on samples with a lamellar structure containing different alpha-platelet thicknesses at temperatures of 715-900 degreesC. The flow stress-versus-strain rate curves for all the microstructures were well fit with an inelastic-deformation equation describing grain-matrix deformation (GMD) (dislocation glide + dislocation climb). However, for heavily pre-deformed specimens, grain-boundary sliding (GBS) as well as GMD was evident. The GBS rate was found to be most rapid for the microstructure with the thinnest alpha laths/platelets. Softening of heavily deformed material was attributed to a decrease in the internal-strength variable sigma* associated with reduced alpha-beta interface strength and to the occurrence of GBS. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.X1170sciescopu

Constitutive analysis of the high-temperature deformation mechanisms of Ti-6Al-4V and Ti-6.85Al-1.6V alloys

The high-temperature deformation mechanisms of a near-alpha titanium alloy (Ti-6.85Al-1.6V) and an alpha + beta titanium alloy (Ti-6Al-4V) were deduced within the framework of inelastic-deformation theory. For this purpose, load-relaxation tests were conducted on the two alloys at temperatures ranging from 750 to 900 degrees C. The stress versus strain rate curves of both alloys were well fit with inelastic-deformation equations which consisted of grain-matrix deformation (GMD) and grain-boundary sliding (GBS). The constitutive analysis revealed that the grain-boundary sliding resistance is higher in the near-alpha alloy than in the two-phase alpha + beta alloy due to the difficulty in relaxing stress concentrations at the triple-junction regions in the near-alpha alloy. In addition, the internal-strength parameter (sigma*) of the near-alpha alloy was much higher than that for the alpha + beta alloy, thus implying that dislocation emission/slip transfer at alpha/alpha boundaries is more difficult than at alpha/beta boundaries. (c) 2004 Elsevier B.V. All rights reserved.X1130sciescopu

High-temperature deformation and grain-boundary characteristics of titanium alloys with an equiaxed microstructure

The high-temperature deformation behavior of single-phase a (Ti-7.0Al-1.5V), near-a (Ti-6.85Al-1.6V), and two-phase (Ti-6Al-4V) titanium alloys with an equiaxed microstructure was examined, and the results were compared within the framework of an internal-variable theory of inelastic deformation. For this purpose, load-relaxation and tension tests were conducted at various temperatures. Stress-strain-rate curves obtained by load-relaxation tests for the three alloys were well described by the equations for grain-matrix deformation and grain-boundary sliding. With respect to boundary strength, the internal-strength parameter (sigma*) for alpha-alpha boundaries was found to be similar to 2 times higher than that for alpha-beta boundaries. The friction stress parameter (Sigma(g)) of boundaries was the highest in the single-phase alpha alloy and the lowest in the two-phase (alpha + beta) alloy. This indicates that grain-boundary sliding occurs preferentially at alpha-beta interfaces rather than at alpha-alpha boundaries. (C) 2007 Elsevier B.V. All rights reserved.X1124sciescopu