Efficient Drilling of Amorphous Alloy Foils Using Low-Energy Long Pulses of a Nd:YAG Laser

Laser drilling of amorphous alloy foils was conducted using low-energy long-pulses (LP) generated using a Nd:YAG laser. Results showed that LP can drill an amorphous alloy foil more efficiently than a nanosecond pulse (NSP) can: an LP at 1 mJ can open a through-hole on an amorphous alloy foil with 25 mm thickness although single shot NSP at 20 mJ formed a crater with ca. 3 mm depth. From these findings, we infer that the markedly higher drilling efficiency of a low-energy LP than that of NSP is attributable to 1) lower plasma generation by LP than by NSP, and 2) repeated irradiation of the target material by multiple sub-pulses in an LP. Results also demonstrate that low-energy LP drilling is applicable to various metal foils and that the drilling efficiency depends on the metal species.

XGBoost automates the characterisation of reversibly actuating planar-flow-casted NiTi shape memory alloy foil

Nickel-Titanium (NiTi) shape memory alloys (SMAs) are smart materials able to recover their original shape under thermal stimulus. Near-net-shape NiTi SMA foils of 2 meters in length and width of 30 mm have been successfully produced by a planar flow casting facility at CSIRO, opening possibilities of wider applications of SMA foils. The study also focuses on establishing a fully automated experimental system for the characterisation of their reversible actuation, significantly improving SMA foils adaptation into real applications. Artificial Intelligence involving Computer Vision and Machine Learning based methods were successfully employed in the development of the automation SMA characterisation process. The study finds that an Extreme Gradient Boosting (XGBoost) Regression model based predictive system experimented with over 175,000 video samples could achieve 99% overall prediction accuracy. Generalisation capability of the proposed system makes a significant contribution towards the efficient optimisation of the material design to produce high quality 30 mm SMA foils.

Microstructure formation and mechanical properties of isothermally-solidified titanium alloy joints brazed by a Ti – Zr – Cu – Ni – Be amorphous alloy foil

Two titanium alloys, OT4 and VT6-c, with a pseudo-α and α + β structure, respectively, were brazed using transient liquid phase (TLP) bonding. To obtain high strength joints an amorphous foil (Ti – 12Zr – 22Cu – 12Ni – 1.5 Be – 0.8V wt.%) was used. Based on microstructural studies and analysis of two- and three-component phase diagrams, the mechanism of the microstructural evolution of the brazed seams of titanium alloys OT4 and VT6-c is described. Brazing at 800 °C with exposure for 0.5 h leads to the formation of a heterogeneous structure consisting of Widmanstätten, eutectoid, and eutectic. Brazed OT4 and VT6-c joints with the presence of a eutectic layer in the centre show low mechanical properties; their ultimate strength lies in a range from 200 to 550 MPa. Increasing the brazing temperature to 840 °C and the exposure time to 2 h, leads to the disappearance of the brittle eutectic component from the seam. This structure typically consists of Widmanstätten with a small number of eutectoid fractions. Joints with the absence of a eutectic layer in the brazed seam demonstrate a strength equal to the base titanium alloys. In this case, failure occurs in the base metal. For brazed samples from the OT4 alloy, the tensile strength value is σb = 750 ± 3 MPa, and for samples from VT6-c, σb = 905 ± 3 MPa. This work was supported by Competitiveness Growth Programme of the Federal Autonomous Educational Institution of Higher Education National Research Nuclear University MEPhI (Moscow Engineering Physics Institute).