Structural-phase and stressed state of vacuum-arc-deposited nanostructural Mo-N coatings controlled by substrate bias during deposition

Abstract

At present, there is an obvious lack of data on the influence of the parameters of the vacuum arc reactive plasma spray deposition process on the phase compo sition, structure, and stress state of widely used nitride coatings. The main attention so far has been devoted to the deposition of transition metal nitrides with high enthalpies of formation, such as TiN, ZrN,. However, under certain conditions, it is also possible to ensure high functional (in particular, mechanical) properties for vacuum arc deposited transition metal nitrides in systems with relatively low enthalpies of formation, such as Cr-N [5] and Mo-N [1]. In the latter case, it should be noted that, based on the thermodynamics of nitride formation in the Mo-N system, a gain in the free energy for the formation of a Mo 2 N phase amounts to 37 kJ/mol and that for δ MoN is 34 kJ/mol [6]. Therefore, it can be expected that, at a relatively low pressure of nitrogen contain ing atmosphere (and, hence, relatively low content of nitrogen in the deposit), the formation of Mo 2 N should be thermodynamically somewhat more favor able than the formation of δ MoN [2, 7].Thus, relatively low enthalpies of formation for compounds of the Mo-N system can lead to a strong dependence of the structural phase and elastically stressed state on the conditions of material formation, in particular, on the energy factor. For highly ionizing methods of vacuum arc plasma deposition of coat ings, this factor is determined to a considerable degree by the negative bias potential (U b ) applied to a sub strate during the deposition process [2,8]. In order to study this influence, we have obtained a series of Mo-N coatings on a Bulat 6 vacuum arc setup [1] at vari ous negative bias potentials, including a floating regime with U b = -(5-8) V and constant bias regimes with U b = -40 and -200 V.Based on the results of previous investigations [1,9,10], optimum conditions for the deposition of Mo-N coatings with high mechanical characteristics (strength, adhesion, friction coefficient) are provided by an arc discharge current of I d = 160 A and a focus ing magnetic field of 75 Oe. The pressure of a reactive nitrogen containing atmosphere was 0.08 or 0.2 Pa. The substrate temperature during deposition did not exceed 350°C, which made it possible to obtain depos its in highly stressed structural states. The evaporated target material was high purity molybdenum of the MChVP grade. The coatings were deposited onto pol ished substrates of 12Kh18N9T chromium-nickel stainless steel, nickel (4 mm thick plates), and copper (5 mm thick plates and 0.2 mm thick foil). After evacuation of the vacuum chamber to a residual pres sure of ~1 × 10 -3 Pa, the surface of substrates was cleaned and activated by bombardment with Mo ions for 3-4 min at a negative bias potential of 1000 V and an arc discharge current of 105 A. Immediately after this preparation, reactive atmosphere was admitted and vacuum arc plasma spray coatings with thick nesses of 0.7-1.1 and 6-7 μm were deposited.Abstract-The effect of su...

Arc-Evaporated Nanoscale Multilayer Nitride-Based Coatings for Protection Against Wear, Corrosion, and Oxidation

“…Results of scientific researches show the tendency of active use of nitrides and borides of transition metals and their combination in the development of protective materials [16][17][18][19][20][21][22][23][24][25]. While nitrides of single elements are studied well enough, their multilayer modifications need study that is more detailed [26][27][28][29][30][31][32][33][34][35].…”

Влияние потенциала смещения и давления азотной атмосферы на структуру и свойства вакуумно-дуговых (Мо+Ti6%Si)N покрытий

“…1, a) и увеличение потенциала U SP (рис. 1, b) при осаждении приводит к уменьшению толщины покрытия, что может быть следствием интенсификации процессов вторичного распыления [4]. Эти же процессы обусловливают и изменения элементного состава.…”

“…3) свидетельствуют, что относи-тельное обогащение покрытия наиболее сильным нит-ридообразующим элементом Ti происходит при наи-меньшем давлении азота. В этих условиях вероятность столкновения атомов в межэлектродном промежутке с потерей энергии мала, и в результате бомбардировки высокоэнергетичными частицами наиболее интенсивно протекают процессы вторичного распыления [4,11].…”

“…Проблему достижения необходимых функ-циональных свойств во многих случаях можно решить путем осаждения сравнительно тонких (до 10 µm) мно-гоэлементных покрытий [1][2][3]. При вакуумно-дуговом методе их получения наиболее высокие свойства (преж-де всего механические) на сегодняшний день реализова-ны в многоэлементных покрытиях на основе нитридов переходных металлов [4][5][6][7][8].…”

Results of approbation of the innovative method of ion nitriding for steels with low temperatures of tempering

“…It was established [5] that in the case of surface modification by applying coatings, the destruction of the system coating-base begins essentially from the plastic deformation of substrate layer near the interface boundary [6]. In order to improve functional properties, they use in such cases creation of special phase [7] or structural [8] states, composite materials [9] and strengthening of boundaries through the distribution of "useful additives" [10].…”