Improving the surface characteristics of Ti-6Al-4V and Timetal 834 using PIRAC nitriding treatments

Abstract

Despite the popularity of a number of techniques of thermochemical diffusion for titanium, in many cases the surface engineering processes used may not be economically viable options for industry. This work focuses on the application of Powder Immersion Reaction Assisted Coating (PIRAC), a relatively inexpensive nitriding treatment that is capable of providing a remarkable improvement in the surface characteristics of titanium alloys. The aim of this work was to determine whether PIRAC could be successfully applied to Ti-6Al-4V and the high-performance near-titanium alloy Timetal 834. In order to study the response of these materials to PIRAC nitriding, techniques such as X-ray diffraction, micro-indentation hardness, surface profilometry, optical and electron microscopy, nano-scratch adhesion testing and ball-on-plate reciprocatingsliding wear testing were employed. These techniques highlighted the markedly different response between the two alloys to the PIRAC treatment; namely, that Ti-6Al-4V forms a thick compound layer, while at the same processing temperature and time Timetal834 does not form any appreciable Ti 2 N phase instead forming a nitrogen-diffusion case with a thin TiN compound layer at the surface. This inherent difference in nitridability influences the metallurgical response of each alloy. Despite this, the surfaces of both alloys were still hardened considerably and their tribological performance in dry sliding conditions improved compared to the untreated alloys.

A Tool for Studying the Mechanical Behavior of the Bone–Endoprosthesis System Based on Multi-scale Simulation

“…Figure 6a shows that at the moment of contact of two rough surfaces of different relief, but of the same roughness, the peak of the friction coefficient occurs, then the process goes to the stationary mode and the friction coefficient becomes almost constant. The plot shows that the greatest coefficient of friction μ 3 = 0.3 is observed on the surfaces of the TiN coating in the first and third deposition modes, which corresponds to the experimental data [43], and the minimal μ 2 = 0.25 in the second deposition mode. The thickness of the quasi-liquid mixing layer for the first and second regime is 0.08 µm, for the third regime-0.12 m.…”

Rapid Nitriding of Titanium Alloy with Fine Grains at Room Temperature

“…In contrast, the strength of Ti alloys is reduced by grain coarsening during the nitriding process because nitriding of Ti alloys is generally performed at a high temperature (≈1173 K) to increase the nitrogen (N) diffusion rate. [2][3][4][5][6] Thus, lowtemperature nitriding has been proposed as a method for suppressing the grain coarsening of Ti alloys and has already been found to increase the fatigue limit of Ti-6Al-4V alloy and form a hard surface layer. [3,4] Tang et al reported that the Gibbs free energy change for the formation of nitrides became negative after a surface mechanical attrition pretreatment; they thereby successfully nitrided Fe at a lower temperature of 573 K. [7,8] However, reducing the nitriding temperature results in long nitriding durations because of the reduction of the N diffusion rate, which is problematic.…”

“…[ 1 ] In contrast, the strength of Ti alloys is reduced by grain coarsening during the nitriding process because nitriding of Ti alloys is generally performed at a high temperature (≈1173 K) to increase the nitrogen (N) diffusion rate. [ 2–6 ] Thus, low‐temperature nitriding has been proposed as a method for suppressing the grain coarsening of Ti alloys and has already been found to increase the fatigue limit of Ti–6Al–4V alloy and form a hard surface layer. [ 3,4 ] Tang et al.…”

Investigation into Microstructure, Wear Resistance in Air and NaCl Solution of AlCrCoNiFeCTax High-Entropy Alloy Coatings Fabricated by Laser Cladding

“…Moreover, when they are used in a harsh corrosive circumstance, the chemical dissolution will further accelerate their failure [4,5]. Many surface modification methods have been utilized to improve the wear resistance of some steels by preparing a high-hardness coatings on them (such as plasma metallizing technique [6], ion chemical heat treatment [7,8], ion deposition [9,10], thermal spraying [11], electroplating [12], magnetron sputtering [13], spark deposition [14] and electron beam treatment [15][16][17]). However, coatings prepared by the above methods usually have loose microstructures, small thickness and poor bonding with the substrate, which limit their applications under harsh circumstances.…”