A guidewire (10) and a method for its manufacture, wherein at least the distal portion (18) of the guidewire (10) comprises an element made of a precursor of a superelastic alloy such as a Ni-Ti linear elastic alloy. The element exhibits a stress-strain curve with a linear stress-strain relationship and a yield point. At room temperature to body temperature the precursor is in the martensitic phase. The distal portion (18) of the guidewire (10) is deformable beyond the yield point by the physician in the field to a desired set shape and exhibits resistance to kinking during insertion into the body as a result of its elasticity.

High elongation linear elastic guidewire

The effects of pulsed gas tungsten arc welding parameters on the morphology of additive layer manufactured Ti6Al4V has been investigated in this study. The peak/base current ratio and pulse frequency are found to have no significant effect on the refinement of prior beta grain size. However, it is found that the wire feed rate has a considerable effect on the prior beta grain refinement at a given heat input. This is due to the extra wire input being able to supply many heterogeneous nucleation sites and also results in a negative temperature gradient in the front of the liquidus which blocks the columnar growth and changes the columnar growth to equiaixal growth.

/pdf/morphology-investigation-on-direct-current-pulsed-gas-275rnf7gw2.pdf

Morphology investigation on direct current pulsed gas tungsten arc welded additive layer manufactured Ti6Al4V alloy.

A β-titanium alloy with extra high strain-hardening rate: Design and mechanical properties

Microstructure control by thermomechanical processing in β-Ti–15–3 alloy

Additive Manufacturing (AM) is an innovative manufacturing process which offers near-net shape fabrication of complex components, directly from CAD models, without dies or substantial machining, resulting in a reduction in lead-time, waste, and cost. For example, the buy-to-fly ratio for a titanium component machined from forged billet is typically 10-20:1 compared to 5-7:1 when manufactured by AM. However, the production rates for most AM processes are relatively slow and AM is consequently largely of interest to the aerospace, automotive and biomedical industries. In addition, the solidification conditions in AM with the Ti alloy commonly lead to undesirable coarse columnar primary ? grain structures in components. The present research is focused on developing a fundamental understanding of the influence of the processing conditions on microstructure and texture evolution and their resulting effect on the mechanical properties during additive manufacturing with a Ti6Al4V alloy, using three different techniques, namely; 1) Selective laser melting (SLM) process, 2) Electron beam selective melting (EBSM) process and, 3) Wire arc additive manufacturing (WAAM) process. The most important finding in this work was that all the AM processes produced columnar ?-grain structures which grow by epitaxial re-growth up through each melted layer. By thermal modelling using TS4D (Thermal Simulation in 4 Dimensions), it has been shown that the melt pool size increased and the cooling rate decreased from SLM to EBSM and to the WAAM process. The prior ? grain size also increased with melt pool size from a finer size in the SLM to a moderate size in EBSM and to huge grains in WAAM that can be seen by eye. However, despite the large difference in power density between the processes, they all had similar G/R (thermal gradient/growth rate) ratios, which were predicted to lie in the columnar growth region in the solidification diagram. The EBSM process showed a pronounced local heterogeneity in the microstructure in local transition areas, when there was a change in geometry; for e.g. change in wall thickness, thin to thick capping section, cross-over?s, V-transitions, etc. By reconstruction of the high temperature ? microstructure, it has been shown that all the AM platforms showed primary columnar ? grains with a ? || Nz fibre texture with decreased texture strength from the WAAM to the EBSM and SLM processes. Due to a lack of variant selection, the room temperature ?-phase showed a weaker transformation ?-texture compared to the primary ?-texture with decreased texture strength in line with the reduction in ?-texture strength.The large ? grains observed in the WAAM process were not significantly affected by changes in the GTAW (Gas Tungsten Arc Welding) process parameters, such as travel speed, peak to base current ratio, pulse frequency, etc. However, an increased wire feed rate significantly improved the grain size. Another important finding from this work was that by combining deformation and AM the grain size was reduced to a greater extent than could be achieved by varying the arc or, heat source parameters. It has been shown that the large columnar ?-grain structure usually seen in the WAAM process, with a size of 20 mm in length and 2 mm in width, was refined down to ~ 150 �m by the application of a modest deformation, between each layer deposited. The EBSM process showed consistent average static tensile properties in all build directions and met the minimum specification required by ISO 5832-3 (for the wrought and annealed Ti6Al4V). The WAAM samples produced using more effective shielding and the standard pulsed GTAW system also showed average static properties that met the minimum specification required by AMS 4985C for investment casting and hipped Ti6Al4V alloy. Overall, the fatigue life of the samples that were produced by AM was very good and showed a better fatigue performance than the MMPDS design data for castings. However, there was a large scatter in the fatigue life due to the effect of pores.

Microstructure, texture and mechanical property evolution during additive manufacturing of Ti6Al4V alloy for aerospace applications

Tensile, fracture toughness, and high cycle fatigue tests were done at 293, 77, and 4 K for Ti-6Al-4V alloys with three levels of oxygen content. The alloys were investigated both in as-forged condition and in the rolled condition. Rolling did not necessarily make α grains finer, but changed the shape from plate-like to globular. Strengths depended mainly on the oxygen content; the lower content produced lower strengths. The alloy with lowest oxygen content showed the best ductility at 4 K. The fracture toughness at cryogenic temperature was also enhanced by the reduction of oxygen. In the lowest oxygen alloy, no drop in the fracture toughness was observed between 293 and 4 K. Fatigue properties were influenced by the forming process. The rolled materials had higher fatigue strength than the forged materials. The difference was accentuated at 4 K. This is believed to be due to the difference in the morphology of α grains. The lowest oxygen alloy showed the highest fatigue strength at 4 K.

Cryogenic mechanical properties of Ti-6Al-4V alloys with three levels of oxygen content

We have discussed the rule by which the predominant cold deformation modes of metastable β phase are governed depending on their chemical compositions through the examinations of the effects of Sn, Al, and Zr on β-quenched and slightly cold rolled microstructures in a Ti-V based alloy system. It seems in Ti-V binary alloys, that orthorhombic martensitic transformation temperatures Ms and Md are depressed far below room temperature by the athermal ω phase at over about 15%V. Tin and aluminum intrinsically lower these temperatures like vanadium. On the other hand, tin and aluminum simultaneously suppress the athermal ω phase of Ti-16V to first rise Md and even Ms up to above room temperature, respectively. The deformation mode of β phase consequently depends on both the Md temperature and the degree of suppression of the athermal ω phase formation. Alloys having a Md above room temperature undergo stress-induced martensitic transformation. As for alloys having a Md below room temperature, alloys where the athermal ω phase is sufficiently suppressed undergo slip, whereas alloys where it is not so done {332} twinning. Since aluminum strongly suppresses the athermal ω formation, increased Al additions change the deformation mode of Ti-16V from {332} twinning to stress-induced martensitic transformation via a quenched α'' region or that of Ti-16V-4Sn from stree-induced martensitic transformation to slip. On the other hand, since tin does not suppress it so much as aluminum, increased Sn additions first change the deformation mode of Ti-16V from {332} twinning to stress-induced martensitic transformation but subsequently revive {332} twinning again before slip. The deformation mode of Ti-V-Al-Sn alloys can be interpreted by superposing the effects of V, Al, and Sn. Zirconium also depresses martensitic transformation temperatures and Ti-14V-6Zr undergoes stress-induced martensitic transformation. However, Ti-16V based Zr-added alloys undergo {332} twinning in the wide range of Zr content because the athermal ω phase formation is rarely suppressed by zirconium. This interpretation has solved the discrepancy of the transition of deformation modes of β titanium alloys.

Effects of alloying elements on deformation mode in Ti-V based β titanium alloy system

S-N curves of Ti-5Al-2.5Sn ELI alloy were determined at liquid helium temperature (4K) for both the base and welded materials.The base material had a longer fatigue life at 4K than at 77K. Welding deteriorated the fatigue properties at 4K. Internal crack initiation was seen at lower cyclic stress in both the base and the welded materials. For the base material, internal crack initiation occurred at 4K, and there were no obvious defects near the initiation sites. On the other hand, fatigue cracks generally initiated at porosity in the weldment. Internal crack initiation is considered one of the causes of reduced fatigue life.High cyclic frequency brought about a large temperature increase in the specimen, making the testing temperature uncertain in fatigue tests at cryogenic temperature.

Fatigue Fracture of Ti-5Al-2.5Sn ELI Alloy at Liquid Helium Temperature

PURPOSE:To produce high-purity high melting point metals, etc., by subjecting the high melting point metals produced with alkali metals, alkaline earth metals, rare earth metals, Al, and Si as reducing agents to melting in an electron beam melting device and subjecting the melt to electron beam irradiation until the characteristic X-ray intensity intrinsic to the reducing agents in the X-ray spectra of the molten metal decreases to 0. CONSTITUTION:The reducing agents such as alkali metals, alkaline earth metals, rare earth metals, Al, and Si usually remain more or less in the product metals if the high melting point metals such as V, Nb, Ta, Mo, and W and active metals such as Ti and Zr are produced by reduction from the raw materials thereof using the above-mentioned reducing agents. The high melting point metals or active metals 1 contg. the residual reducing agents are put into a vessel 3 in a shielding case 4 and after the inside of the case 4 is evacuated to a vacuum, an electron beam is projected from the electron beam irradiation device 5 on the metals to melt the same. The X-ray intensity of the residual reducing agents in the molten metal M is detected by an X-ray detector 6 during the melting process and the electron beam irradiation is continued until the intensity decreases to zero. The residual reducing agents are thus removed without lowering the yield of the molten metal and the high-purity high melting point or active metals are produced.

Electron beam melting method

PURPOSE:To continuously execute a surface treatment and hot rolling and to improve productivity and the reliability of a product by irradiating electron beams on the surfaces of a high-temp. ingot drawn from a casting mold of an electron beam melting and casting device then immediately passing the ingot between surface forming rolls. CONSTITUTION:Electron beam irradiating devices 11, 11 are disposed toward the surface layer part of the ingot 6 below the water-cooled casting mold 3 of the electron beam melting and casting device body 1. A pair of the surface shaping rolls R, R are disposed with the mold 6 in-between to the lower part of the position where the electron beams are irradiated. The electron beams are irradiated from the devices 11, 11 toward the ingot 6 in the high-temp. state to remelt only the surface layer parts and thereafter the ingot is immediately grasped under the pressure by the rolls R, R to push and follow the molten metal in the projecting part toward the recess side, by which the ruggedness on the surface is smoothed and the smooth surface characteristic is obtd. The surfaces are thus smoothed by utilizing the heat posessed by the ingot 6 right after the ingot is drawn from the casting mold and by the min. output of the electron beams and the pressing pressure of the shaping rolls after the remelting.

Nishimura Takashi

Papers

Cryogenic mechanical properties of Ti-6Al-4V alloys with three levels of oxygen content

Effects of alloying elements on deformation mode in Ti-V based β titanium alloy system

Fatigue Fracture of Ti-5Al-2.5Sn ELI Alloy at Liquid Helium Temperature

Electron beam melting method

Continuous casting method