Fabrication of NiTi shape memory alloy by Micro-FAST

Abstract

Abstract.A NiTi shape memory alloy, known as nitinol, has been intensively studied for last five decades. The NiTi alloy with large size is commonly produced by vacuum sintering, thermal explosion mode of self-propagating high-temperature synthesis (TE-SHS) and spark plasma sintering (SPS). These methods are, however, rarely utilized for the forming of miniature and micro-sized components and have their own limits and disadvantages, such as long process chains and low efficiency with the processes. In the study reported in this paper, an innovation in rapid powder consolidation technology, called Micro-FAST (combining micro-forming and electric-current activated sintering techniques (FAST)) is introduced for the forming of micro-components in which the loose powders are loaded directly into the die, followed by electric-sintering. In the study, 4.0 mm × 4.0 mm miniature cylinders were formed with pre-alloyed NiTi powders. Sintered sample with relative density of 98.65% has been fabricated at a sintering temperature of 1150°C in a relatively short cycle time (119.5 s). Based on the results of SEM and XRD, it was found that the densified samples with Ni 3 Ti, NiTi and NiTi 2 phases were produced.

Integrated, multidisciplinary approaches for micro-manufacturing research, and new opportunities and challenges to micro-manufacturing

“…49 More micro-parts formed with and developing process understanding of Micro-FAST were reported in the literatures. 29,[50][51][52][53][54] The main techniques that were developed for overcoming barriers of the traditional FAST for the applications at the micro-scale including (1) directly feeding loose powders into the dies/moulds (i.e. no need for preparing a green compact); (2) combining micro-forming (forming the component at the microscale) with the FAST to enable complex shapes/features at the micro-scale, being assisted using large current density; and (3) directly forming the component using the shaping dies/moulds without using lubricants.…”

“…Micro-FAST project resulted in a completely new manufacturing system for the volume production of miniaturised/micro-components by overcoming the challenges on the manufacturing of these components with a wide range of materials 55 (e.g. metallic alloys, and composites and ceramics) [51][52][53][54] that are normally seen as 'difficult-to-cut' and 'difficult-to-deform' materials, through (1) developing the Micro-FAST laboratory process into a high throughput, flexible and costefficient production process involving simultaneous micro-forming and electric-field activated sintering of powder materials; (2) developing technological measures for scaling up the process for improved forming quality and efficiency; (3) developing an automated industrial press system for Micro-FAST-based micro-/ nano-manufacturing, including fully automated modes for heating, cooling, vacuum, measurement, condition monitoring as well as tool transport. These were enabled/supported by developing (1) a new press machine with an innovative handling-system, (2) an innovative inline monitoring and inspection system, (3) innovative multi-scale modelling techniques for the analysis of densification and forming processes, (4) new tool designs and micro-tooling techniques for highperformance tools, and (5) high-quality nano-material systems.…”

“…Photos of the sample parts formed with Micro-FAST. [46][47][48][49][50][51][52][53] energy savings, cost and waste reduction and materialrecycling issues, which were studied thoroughly through an expertise life-cycle assessment. First Micro-FAST prototype production machine system has been built, tested and demonstrated, and continuing optimisation of the machine system and tool designs is being carried out, aiming at fully meeting industrial production requirements.…”