Thermal stability of electrodeposited LIGA Ni–W alloys for high temperature MEMS applications

Abstract

For thermally stable LIGA materials for high temperature MEMS applications LIGA Ni-W layers and micro testing samples with different compositions (15 and 5 at% W) were electrodeposited. In order to investigate the thermal stability the Ni-W layers were annealed at different temperatures (300-700°C) and for different durations (1, 4, 16 h). Their microstructure and microhardness were than analysed after annealing and compared with those of as-deposited states. The observed microstructures show, in comparison to pure LIGA nickel, a small grain growth and a relatively stable structure up to 700°C. The micro-hardness values of the LIGA Ni-W layers are higher than those of the pure LIGA nickel. The micro-hardness measurements for high W-content show in addition a low decrease of the hardness values with increase of the annealing duration. Tensile tests were carried out for each composition (5 and 15 at%). Ni-W shows higher strength (UTS) above 750 MPa and 1,000 MPa, respectively and lower ductility than pure nickel.

Emerging materials for microelectromechanical systems at elevated temperatures

“…[86][87][88][89] Table I summarizes the mechanical properties of several binary Ni-alloys in comparison with pure LIGA Ni. 85,86,[90][91][92] The as-deposited strengths are quite good; however, challenges with sulfur grain boundary segregation and grain coarsening limit the utility of the Ni-Fe 85 and Ni-Co 86,90 systems at elevated temperatures. While Ni-Mn performs well even after thermal annealing, maintaining a significant fraction of the as-deposited strength and a very respectable ductility, 86 the magnetic properties and lower density of this alloy have limited its implementation.…”

“…This leaves the Ni-W system, which has somewhat limited ductility in the as-deposited condition 93 but has excellent thermal stability and high density. 91,92 Originally considered for coating applications due to its superior corrosion and wear resistance, 94-96 electrodeposited nanocrystalline Ni-W is a promising candidate for structural elements in MEMS. 91,92,97 Figure 8, from Haj-Taieb et al, 91 illustrates the improvement in mechanical performance at elevated temperatures.…”

Application of Electroforming Process to Bulk Amorphous Ni-W Alloy

“…1) Thus, the amorphous Ni-W alloy film is one of the candidates for MEMS devices. 2,3) In application of amorphous Ni-W alloy to the MEMS devices, the reliability of the mechanical properties is of great necessity. One of the important factors for high reliability is homogeneity of the composition.…”

Anti-corrosion and microstructural properties of Ni–W alloy coatings: effect of 3,4-Dihydroxybenzaldehyde

“…Significant interest in the development of nanocrystalline Ni-W alloy as surface coatings is receiving considerable attention, since its potential applications are in multiple [5]. This alloy system has become an ideal choice in the industrial sector, owing to its remarkable properties like noticeable corrosion resistance [6], better electrocatalytic property [7] combination of desired hardness and wear resistance [8], stability at higher temperatures [9] and as a effective barrier in electronic/electrical components [10], and moreover this alloy coatings were nominated as a propitious and challenging alternative to the hazardous hard chrome plating [11, 12]. The beneficial exploit of Ni–W alloys to the materials which require resistant to the relatively high temperatures, includes micro and nano-electromechanical systems, sliding contacts or high-temperature superconductors [13, 14].…”