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This research examines how pulse-on time and servo voltage affect the machining behavior and phase transformation of a shape memory alloy during WEDM.

June 4, 2026Open Access

Machining behavior and phase transformation in WEDM of Ti₅₀Ni₄₉Co₁ shape memory alloy

HSHargovind SoniGalgotias University RKR Suresh Kumar GKG N KumaraswamyAmrita Vishwa Vidyapeetham

Key Points

This research examines how pulse-on time and servo voltage affect the machining behavior and phase transformation of a shape memory alloy during WEDM.
Experiments conducted using a Taguchi L 25 orthogonal array to assess pulse-on time and servo voltage effects.
Measurements included material removal rate (MRR), surface roughness (Ra), and XRD analysis for phase changes.
3D surface profilometry assessed morphological changes during the machining process.
Peak MRR reached 8.43 mm3/min with Ton = 125 µs and SV = 20 V, while surface roughness increased from 2.85 μm to 5.01 μm.
XRD analysis revealed secondary phases (NiTi2, TiO2, CuZn) formed during machining due to oxidation.
DSC results indicated no loss of shape-memory properties in bulk material despite variations in transformation behavior.

Abstract

Abstract The study reported in this research article focuses on the machining behavior and phase transformation of Ti₅₀Ni₄₉Co₁ shape memory alloy during wire-electrical-discharge-machining (WEDM). Experiments were performed to determine the combined effect of the pulse-on time (Ton) and servo voltage (SV) under high-energy discharge conditions, using a Taguchi L 25 orthogonal array. The results show that the pulse-on time significantly increases discharge energy, which reached a peak MRR of 8.43 mm 3 /min with Ton = 125 µs and SV = 20 V (Run order 21). However, it also increased the surface roughness (Ra) from 2.85 μm to 5.01 μm, producing deeper craters and hardened recast layers as well as re-solidified debris because of rapid melting and solidification. Major morphological changes were observed at high discharge energy, as confirmed by 3D surface profilometry. The servo voltage influenced the stability of the spark: higher voltages reduced discharge intensity, resulting in lower material removal rate but improved surface finish. XRD analysis revealed the formation of secondary phases, containing NiTi 2 , TiO 2 , and CuZn, was produced during machining, resulting from oxidation and transfer of the electrode material. DSC examination showed an increase in transformation peaks, a decrease in transformation enthalpy, and an insignificant change in transformation temperatures, indicating that the martensitic transformation in the recast layer was partially suppressed by compositional alterations and oxide formation. Nevertheless, no loss of shape-memory property was observed in the bulk material, although slight variations in transformation behavior were observed. Overall, the results support the importance of properly optimizing pulse-on time and servo voltage to achieve a balance among good machining performance, consistent surface quality, and good functional performance, particularly in precision biomedical, aerospace, and smart actuator applications.

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