Evaluating the effects of PIRAC nitrogen-diffusion treatments on the mechanical performance of Ti–6Al–4V alloy

Abstract

a b s t r a c tPowder Immersion Reaction Assisted Coating (PIRAC) is a relatively simple nitrogen diffusion based process which has been proposed as a technique capable of considerable improvements in the tribological performance of ceramics and metals alike; however, the necessary exposure of the substrate material to high temperatures for several hours may have an adverse effect on the bulk properties of materials such as titanium alloys. The effect of PIRAC treatments on the bulk metallography and mechanical properties of Ti-6Al-4V has been studied. Following PIRAC nitrogen-diffusion treatment, studies using X-ray diffraction and cross-sectional microscopy have shown evidence of the formation of a thin ( $ 1.4 mm) TiN/Ti 2 N layer, together with the presence of some Ti 3 Al intermetallic phase. Semilogarithmic S-N plots show a deleterious effect after PIRAC treatment in terms of material cyclic fatigue strength, particularly at higher treatment temperatures. Samples processed at 800 1C for 4 h however exhibit better fatigue performance than others treated at lower temperatures for longer nitriding times. Fractographic inspection has shown that fatigue cracks originate at (or near) the surface for the untreated Ti-alloy and from the subsurface regions following diffusion treatment, owing to the build-up of compressive stresses in the latter, which hinder crack propagation.

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“…It can be seen from Fig. 2 that the hardest is the coating obtained by mode 3, all the curves correspond to experimental data from [24]. Thus, we may conclude that the models of the materials behavior are validated and can be used in further steps in our work.…”

“…From the literature [23], we chose the following values for the material properties of the titanium alloy Ti6Al4V: density ρ = 4420 kg/m 3 , shear modulus G = 41 GPa, bulk modulus K = 92 GPa, Young's modulus E = 110 GPa, yield stress σ y = 0.99 GPa, ultimate strength σ b = 1.07 GPa and ultimate strain ε b = 0.10. Geometric features of the TiN coating and its mechanical properties are determined by the deposition modes at PIRAC [24] forming. Thus, at a deposition temperature of 700º C and a treatment time of 48 hours, the coating on the titanium substrate has a thickness of 1.3 μm with an average roughness height of 0.15 μm (mode 1) and the elastic modulus, depending on the deposition regime, was equal to E 1 = 258 GPa; at a deposition temperature of 800º C and a treatment time of 4 hours the coating on the titanium substrate has a thickness of 1.4 μm with an average roughness height of 0.132 μm (mode 2) and an elastic modulus of E 2 = 258 GPa; at a deposition temperature of 900° C and a treatment time of 2 hours the coating on the titanium substrate has a thickness of 1.5 μm with an average roughness height of 0.265 μm (mode 3) and an elastic modulus of E 3 = 321 GPa.…”

Duplex coatings with enhanced adhesion to Ti alloy substrate prepared by powder immersion nitriding and TiN/Ti multilayer deposition

“…A detailed description of the compound layer can be found in [12]. The hardened zone is clearly observed in the microhardness-depth profile of PIRAC-nitrided Ti6Al4V, Fig.…”

“…Further details of PIRAC-N process can be found elsewhere [10,11]. PIRAC-N time-temperature regime was selected based on its marginal effect ( $ 5% reduction) on fatigue strength of Ti6Al4V [12].…”

ChISLENNOE MODELIROVANIE IZNAShIVANIJa DVUH ShEROHOVATYH POVERHNOSTEJ BIOSOVMESTIMOGO KERAMIChESKOGO POKRYTIJa PRI TRENII

“…Секция 3. Проблемы компьютерного конструирования материалов с иерархической структурой DOI: 10.17223/9785946218412/145 ЧИСЛЕННОЕ МОДЕЛИРОВАНИЕ ИЗНАШИВАНИЯ ДВУХ ШЕРОХОВАТЫХ ПОВЕРХНОСТЕЙ БИОСОВМЕСТИМОГО КЕРАМИЧЕСКОГО ПОКРЫТИЯ ПРИ ТРЕНИИ 1,2 Еремина Г.М., 1,2 Смолин А.Ю. 1 Институт физики прочности и материаловедения СО РАН, Томск 2 Томский государственный университет, Томск…”