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Multi-objective optimization of WEDM process parameters of Ti49.4-Ni50.6 shape memory alloy for orthopaedic implant application

Takale A. M., Chougule N. K.

Archives of Materials Science and Engineering

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2018

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Vol. 93, nr 1

12--31

EN

Purpose: This paper focuses on the investigation on the effect of process parameters such as pulse on time (Ton), pulse off time (Toff), spark gap set voltage (SV), wire feed (WF) and wire tension (WT) on the responses such as the material removal rate (MRR), surface roughness (SR), kerf width (KW) and dimensional deviations (DD) of Ti49.4Ni50.6 (at.%) shape memory alloy (SMA) machined by WEDM. Ti-Ni SMA has fascinating properties and biocompatibility, it is considered for the present work. Design/methodology/approach: As per the Taguchi technique, L18 orthogonal array experiments on WEDM have been performed. The signals to noise (S/N) ratio plots are analysed to determine the influence of process parameters. Analysis has been tested through analysis of variance (ANOVA). SEM images are taken to confirm the results offering better surface quality. Findings: It was observed that pulse on time is the most significant factor for MRR and SR with the contribution of 35.69% and 59.02% respectively. The SV is a significant factor for KW and DD with contributions of 47.35% and 30.03% at 95% confidence level. A multi-response optimization has been carried out using grey relational analysis (GRA) to determine the optimum combination of process parameters. It is shown that, through GRA the optimal machining parameter setting such as A2B1C3D2E1 i.e. (pulse on time of 115 machine unit, pulse off time of 20 machine unit, spark gap set voltage of 90 V, wire feed of 6 m/min and wire tension of 3 machine unit) has been observed for maximum MRR and minimum SR, KW and DD. Young’s modulus checked for biocompatibility. Research limitations/implications: Heat treatment process like annealing is found to be most suitable to recover shape memory effect of WEDMed samples.

2

Temperature measurement as a new technique applied to the phase transformation study in a TiNi shape memory alloy subjected to tension

Gadaj S. P., Nowacki W. K., Pieczyska E. A., Tobushi H.

Archives of Metallurgy and Materials

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2005

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Vol. 50, iss. 3

661-674

EN

Temperature distributions obtained from studying the stress induced phase transformations in a TiNi shape memory alloy (SMA) were employed for the investigation into nucleation and further development of the bands of martensite and reverse transformations. A thermovision camera was used to register the distribution of infrared radiation emitted by the specimen surface and constructed thermograms with of 50 Hz frequency. Basing on temperature changes and the relevant mechanical characteristics it was noticed that just after crossing a certain threshold stress, narrow lines of considerably higher temperature — up to 10 K, corresponding to the martensite phase, appeared starting from the central part of the specimen and developing towards the specimen grips. Their angle of inclination was about 42°. At higher stresses, a few such lines parallel to each other occurred and moved towards the specimen borders, as well as the next “family” of them, developing in the perpendicular direction. The heterogeneous field of the temperature distribution was observed also during the unloading process of TiNi SMA, while the reverse transformation — austenite into martensite, took place. The reverse transformation was accompanied by a significant temperature decrease. The lines of reverse transformation were observed when the unloading process started and developed in the whole material volume, however the process remained inhomogeneous. The processes of relaxation do not bring about any changes in the nature of phase transitions, however, the relaxation involved temperature changes cause stress changes as the deformation (unloading) develops after relaxation.

PL

Pomiary rozkładów temperatury podczas przemiany martenzytycznej i przemiany odwrotnej stopu TiNi z pamiecia kształtu, stymulowanych odkształceniem, wykorzystano do badania inicjacji i rozwoju tych przemian oraz wpływu parametrów odkształcania na te przemiany. Rozkłady temperaury mierzono za pomocą kamery termowizyjnej, umożliwiającej uzyskiwanie obrazów termicznych z częstotliwością do 50 Hz. Na podstawie badań charakterystyk mechanicznych i zmian temperatury stwierdzono, że mertenzytyczna przemiana fazowa rozpoczyna sie pod katem ok. 42° do kierunku rozciągania próbki. W miarę odkształcania pojawia się coraz więcej pasm, zarówno równoległych, jak i skierowanych przeciwnie, aż obejmują one całą próbkę. Skok temperatury w miejscu pojawienia się pojedynczego pasma wynosi ok. 6 K. Przemiana odwrotna jest również procesem niejednorodnym, przy czym w pasmach tej przemiany następuje spadek temperatury. Przyrost średniej temperatury próbki podczas przemiany martenzytycznej może przekraczać 40 K, co powoduje przyrost naprężeń w miarę rozciągania. Procesy relaksacji nie powodują zmian charakteru przemian fazowych, jednak związane z relaksacją zmiany temperatury wywołują zmiany naprężeń przy kontynuacji odkształcania (odciążania) po relaksacji.

3

Shape memory alloy preparation for multiaxial tests and identification of fundamental alloy performance

Tanaka K., Kitamura K., Miyazaki S.

Archives of Mechanics

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1999

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Vol. 51, nr 6

785-803

EN

TiNi shape memory alloy preparation for the multiaxial tests was explained. Stable response of the alloy was realized, not by training but by an effective combination of the alloying technique and the heat treatment: Ti-51.0 at%Ni polycrystalline shape memory alloy heat-treated by annealing at 673 K for 3.6 ks followed by cooling in a furnace. Some preliminary tests were performed to identify the fundamental alloy characteristics: the transformation temperatures, the stress-strain curves at several temperatures and the strain-temperature curves under constant hold stresses.