Intermetallic Phase Evolution of Cold-Sprayed Ni-Ti Composite Coatings: Influence of As-Sprayed Chemical Composition

Abstract

Owing to low-temperature deposition conditions and high deposition rate, cold spray offers unique advantages in manufacturing a wide variety of metallic and composite coatings including metal matrix composites produced from physically blended powders. One of the challenges of producing composite coatings using cold spray is the deviation of coatings composition from the blended feedstock powder composition. This is of utmost importance as it affects the composition and phase evolution of intermetallic forming coatings during post spray heat treatment. In this work, cold spray of composite Ni - Ti coatings and formation of intermetallics from post spray heat treatment were investigated as a first step to examine the potential of producing equiatomic bulk Ni - Ti by cold spray. Three different physically blended Ni and Ti powders mixtures were sprayed on titanium substrates to address the coating composition variation from the blended feedstock powder and study its influence on phase evolution during post spray heat treatment. High-density and well-dispersed composite coatings were achieved for each case. EDS analysis revealed as-sprayed coatings with 10.5, 35.9 and 56.9 at.% Ni (and with balanced Ti ratios) from the three powder mixtures. Annealing treatments were conducted at 400, 500 and 900 °C for 1 and 2 h and comparative studies of the intermetallic compound formations were carried out. Microstructural investigation showed that all three equilibrium intermetallics phases of binary Ni - Ti phase diagram (Ni 3 Ti, Ti 2 Ni and NiTi) formed in the two Ni-rich composite coatings with NiTi phase being maximum in the coating with the closest composition to equiatomic ratio while only Ti 2 Ni phase formed in the Ti-rich coating after annealing. Thermal etching analysis of coatings showed that NiTi phase forms with a gradient microstructure from Ti splats boundary toward the center of splats, which is attributed to the grain refinement of CS samples at splat boundary and intermetallic nucleation mechanism.

Study of the Tribological Properties of Diffusion Coated NiTi Intermetallic on Cp Titanium

“…12 shows the cross sectional micrograph of the worn Cp Ti under an applied load of 40 N. It can be seen that holes and cracks are formed in depth below the surface and eventually result in the formation of debris with a possible delamination mechanism. In fact, by increasing the amount of the applied force, the surface temperature increases due to the heat generated by friction, and as stated in a previous research [26], the yield strength of titanium decreases by increasing temperature and as a consequence, the plastic deformation becomes more severe. Briefly, even under a high load (40N),…”

“…Therefore, applying a diffusion-based treatment, which improves adhesion strength to the substrate, can overcome the defects of the previous methods [25]. Nikbakht et al [26] reported the formation of a composite Ni-Ti coating on the titanium substrate through a cold spray method followed by a heat treatment. Li et al [27,28] proposed a new method for preparing Ni-Ti intermetallic compounds by nickel plating on titanium substrate followed by electron beam remelting.…”

Cold Spray: Over 30 Years of Development Toward a Hot Future

“…The advantage of the CS process in the production of metal matrix composite (MMC) material is the low working temperature, which eliminates oxidation and possible matrix-reinforcement (ceramic, metallic, or intermetallic) interfacial reactions, thus preserving the feedstock material microstructure (Ref 379 ). CS deposition of MMC can be divided into two main categories based on the nature of the reinforcement materials: metal-metal MMCs and ceramic-metal MMCs.…”

Formation of metal composites by detonation spray of powder mixtures

“…Such coatings are used as wear-resistant and corrosionresistant barriers in different domains of industry [1,2]. In some cases, the metal composite coatings are used as the precursors for following heat treatment [3][4][5][6]. Due to the chemical reaction between the coating components during heat treatment, the new phases with unique properties could be formed.…”

“…In this case, the coating is obtained by simultaneous spraying of several low-cost commercially available pure metal or alloy powders. Nowadays the articles devoted to thermal spraying of metal powder mixtures are available [3][4][5][6]11]. However, the main issue limiting the application of thermal spray methods for elaboration of metal composites using the powder blends is the complexity of simultaneous spraying of powders with different thermal properties.…”