The structure and mechanism of formation of the ‘glaze’ oxide layers produced on nickel-based alloys during wear at high temperatures

The structure and composition of the worn surfaces, and in particular of the tribologically important ‘glaze’ region, formed on Nimonic 75, Nimonic C263, Nimonic 108 and Incoloy 901 after sliding in air at elevated temperatures (150–800°C) have been determined. A typical wear scar is comprised of a number of areas, some having a thin, physically homogeneous surface ‘glaze’ layer, the rest having no ‘glaze’ surface. The ‘glaze’ layer lies on top of a region either of highly compacted oxide particles above a growing, steady-state oxide layer, or of alloy, deformed to varying degrees, depending on time of sliding, ambient temperature and the relative strength of the alloy.Electron diffraction shows the surface ‘glazes’ to consist of simple oxides after sliding at temperatures up to 400°C, viz. NiO in that on all four alloys, CoO on N108 and C263, and FeO on Incoloy 901. At the higher temperatures, NiCr₂O₄ is observed in the ‘glaze’ on all the alloys, with NiO and Cr₂O₃ on N75, Cr₂O₃ and probably CoO on C263 and N108 and α-Fe₂O₃, FeO and Fe₃O₄ on Incoloy 901. The ‘glaze’ and underlying, wear-affected, oxidized regions are shown by ion microprobe mass spectrometry, electron spectroscopy and electron probe microanalysis to consist of oxides, containing all the alloying elements, approximately in the same average proportions as in the alloys. Three possible mechanisms for the formation of the observed structure of the ‘glaze’ regions are proposed.It is concluded that high-strength properties and relatively rapid transient oxidation rates at elevated temperatures are desirable qualities in alloys employed under high temperature sliding conditions.     

Effect of the Conditions of the Nanostructuring Frictional Treatment Process on the Structural and Phase States and the Strengthening of Metastable Austenitic Steel

The effect of the multiplicity of frictional loading with a sliding synthetic diamond indenter at room temperature in an argon medium and the temperature of loading in the range of ?196 to +250°C on the phase composition, fine structure, and micromechanical properties of the surface layer of metastable austenitic chromium-nickel steel has been studied. It has been established that the completeness of the strain-induced martensitic γ → α′ transformation in the surface layer of steel is determined by the loading multiplicity and temperature, as well as the level of strengthening grows with an increase in the frictional loading multiplicity, but weakly depends on the frictional treatment temperature. According to the microindentation data, the characteristics of the surface layer strength and resistance to elastic and plastic deformation are improved with an increase in the frictional loading multiplicity. Frictional treatment by scanning with a synthetic diamond indenter at room and negative temperatures provides high quality for the treated surface with a low roughness parameter (Ra = 80.115 nm), and an increase in the frictional loading temperature to 150–250°C leads to the development of a seizure and growth in Ra to 195–255 nm. Using transmission electron microscopy (TEM), it has been shown that frictional treatment results in the formation of nanocrystalline and fragmented submicrocrystalline structures of strain-induced α′-martensite (at a loading temperature of ?196°C) and austenite (at a loading temperature of +250°C) in the surface layer of steel alongside with two-phase martensitic-austenitic structures (at a loading temperature of +20°C).     

Effect of austempering temperature on machinability of Cu–Ni–Mo alloyed austempered ductile iron for heavy section parts

Abstract

The machinability of an austempered ductile iron with a suitable chemical composition for heavy sections has been assessed. Austempering heat treatment was carried out at three temperatures, 300, 340 and 375°C, after austenitising at 870°C for 100?min. Drilling tests, tool wear and surface roughness measurements were used to evaluate the machinability. Drilling operation failure, severe tool wear and the poorer surface roughness of the specimens austempered at lower temperatures indicated that austempering at higher temperatures clearly resulted in better machinability. The machinability of testpieces austempered at 375°C, which contained higher fractions of retained austenite, was superior to that of testpieces autenitised at lower temperatures, indicating that hardness is an important factor in assessing machinability in addition to high carbon austenite content.     

Effect of Friction-Induced Deformation on the Structure,Microhardness, and Wear Resistance of Austenitic Chromium—Nickel Stainless Steel Subjected to Subsequent Oxidation

The effect of plastic deformation that occurs in the zone of the sliding friction contact on structural transformations in the 12Kh18N9T austenitic steel subjected to subsequent 1-h oxidation in air at temperatures of 300–800°C, as well as on its wear resistance, has been studied. It has been shown that severe deformation induced by dry sliding friction produces the two-phase nanocrystalline γ + α structure in the surface layer of the steel ~10 μm thick. This structure has the microhardness of 5.2 GPa. Subsequent oxidation of steel at temperatures of 300–500°C leads to an additional increase in the microhardness of its deformed surface layer to the value of 7.0 GPa. This is due to the active saturation of the austenite and the strain-assisted martensite (α′) with the oxygen atoms, which diffuse deep into the metal over the boundaries of the γ and α′ nanocrystals with an increased rate. The concentration of oxygen in the surface layer of the steel and in wear products reaches 8 wt %. The atoms of the dissolved oxygen efficiently pin dislocations in the γ and α′ phases, which enhances the strength and wear resistance of the surface of the 12Kh18N9T steel. The oxidation of steel at temperatures of 550–800°C under a light normal load (98 N) results in the formation of a large number of Fe₃O₄ (magnetite) nanoparticles, which increase the resistance of the steel to thermal softening and its wear resistance during dry sliding friction in a pair with 40Kh13 steel. Under a heavy normal load (196 N), the toughness of 12Kh18N9T steel and, therefore, the wear resistance of its surface layer decrease due to the presence of the brittle oxide phase.     

Anodic electrolytic-plasma borocarburizing of low-carbon steel

The effect of conditions of anodic electrolytic-plasma borocarburizing of low-carbon steel on its structure and properties has been studied. It has been established that the effect of the treatment conditions on the thickness of a modified layer is explained by the competition of boron and carbon diffusion and steel-sample oxidation. The mechanism of transport of saturating components from electrolyte into steel is described. An electrolyte composition (10–15% sal ammoniac, 5% boric acid, and 4–8% glycerine) and treatment modes (800–900°C, 5 min) are suggested that produce a hardened surface layer with a thickness of up to 0.15 mm and a microhardness of 1000 HV and reduce surface roughness by an order of magnitude. Anodic electrolytic-plasma borocarburizing makes it possible to reduce the coefficient of friction by 36%, steel-wear rate by an order of magnitude, and corrosion rate by 2.5 times.     

The effects of ultrasonic nanocrystal surface modification (UNSM) on pack aluminizing for the fabrication of Pt-modified aluminide coatings at low temperatures

An 8–9 μm thick Pt layer was coated on a superalloy and transformed to a Ni–Pt alloy layer by the interdiffusion of Ni and Pt at 1050 °C for 3 h. The surface of the Ni–Pt alloy layer was pack aluminized to form a Pt-modified aluminide coating. Ultrasonic nanocrystal surface modification (UNSM) was applied to the alloy layer prior to pack aluminizing. The effects of UNSM on Pt-modified aluminide coatings fabricated at 750, 850, 950, and 1050 °C were studied. The treated Ni–Pt alloy layers had finer grain sizes than the untreated specimens. In addition, UNSM made the grain size of the Ni–Pt alloy finer and reduced the surface roughness. During pack aluminizing, the Pt-modified aluminide coatings fabricated following UNSM uptook more Al and were thicker than the untreated Pt-modified aluminide coatings at the various temperatures (750, 850, 950, and 1050 °C). The untreated Pt-modified aluminide coatings with pack aluminizing performed at 750 and 850 °C were composed of only a two-phase (NiAl + PtAl₂) layer, due to insufficient diffusion of Pt at the lower temperatures. However, two-phase and one-phase (NiAl) layers were obtained in the treated Pt-modified aluminide coatings which were pack-aluminized at 750, 850, 950, and 1050 °C, due to the diffusion of Pt through the greater amount of grain boundaries and increased volume generated by UNSM before the pack aluminizing. Additionally, the treated coatings had smoother surfaces even after the pack aluminizing. During cyclic oxidation at 1150 °C for 1000 h, the treated Pt-modified aluminide coatings aluminized at relatively low temperatures (750 and 850 °C) showed better cyclic oxidation resistance than the untreated Pt-modified aluminide coating aluminized at 1050 °C.     

Influence of Plasma Nitriding on the Microstructure, Wear, and Corrosion Properties of Quenched 30CrMnSiA Steel

The oil-quenched 30CrMnSiA steel specimens have been pulse plasma-nitrided for 4 h using a constant 25% N₂-75% H₂ gaseous mixture. Different nitriding temperatures varying from 400 to 560 °C have been used to investigate the effects of treatment temperature on the microstructure, microhardness, wear, and corrosion resistances of the surface layers of the nitrided specimens. The results show that significant surface-hardened layer consisting of compound and diffusion layers can be obtained when the oil-quenched steel (α′-Fe) are plasma-nitrided at these experimental conditions, and the compound layer mainly consists of ε-Fe_2-3N and γ′-Fe₄N phases. Lower temperature (400-500 °C) nitriding favors the formation of ε-Fe_2-3N phase in surface layer, while a monophase γ′-Fe₄N layer can be obtained when the nitriding is carried out at a higher temperature (560 °C). With increasing nitriding temperature, the compound layer thickness increases firstly from 2-3 μm (400 °C) to 8 μm (500 °C) and then decreases to 4.5 μm (560 °C). The surface roughness increases remarkably, and both the surface and inner microhardness of the nitrided samples decrease as increasing the temperature. The compact compound layers with more ε-Fe_2-3N phase can be obtained at lower temperature and have much higher wear and corrosion resistances than those compound layers formed employing 500-560 °C plasma nitriding.     

Effect of severe plastic deformation on the structure,microhardness, and wear resistance of the surface layer of titanium subjected to gas nitriding

The effect of severe plastic deformation under dry sliding friction on the structure, microhardness, and wear rate of the VT1-0 titanium subjected to gas nitriding has been studied. It has been shown that this deformation leads to the formation of a nanocrystalline structure with an α-crystal size of 10–100 nm and a microhardness of ～3.1 GPa in a surface layer up to 10 μm thick. The presence of this structure intensifies the saturation of the surface of the titanium with nitrogen in the course of subsequent gas nitriding at temperatures of 650–750°C. The formation of the nitride nanocrystalline TiN phase in the deformed titanium occurs at a relatively low nitriding temperature (700°C) and a short-term holding (2 h). The volume fraction of the nitride phase, which is formed in the layer up to 10 μm thick, reaches a few tens of percent, which leads to an increase in the microhardness of the nitrided surface of the titanium deformed by friction. Preliminary severe plastic deformation has a negative effect on the fatigue wear resistance of the nitrided titanium due to an increased brittleness of the deformed and subsequently nitrided surface layer of this material.     

Effect of strengthening friction treatment on the chemical composition,structure, and tribological properties of a high-carbon steel

The structure and chemical composition of nanocrystalline layers formed on the surface of a steel U8 with 0.83 wt % C (quenched, as well as quenched and tempered at 200°C) under the conditions of frictional loading by a hard-alloy indenter in different media (gaseous and liquid nitrogen, air) have been investigated by the methods of transmission electron microscopy, X-ray diffraction analysis, nuclear reactions, Rutherford back scattering, and wave- and energy-dispersive microanalyses. Maximum levels of defectiveness (high density of dislocations and point defects) and microhardness of the nanocrystalline structure have been attained upon friction treatment of the low-temperature tempered steel in a liquid-nitrogen medium because of deformation localization in a thin surface layer, intensification of deformation-induced dissolution of the ɛ carbide phase, and saturation of the layer with nitrogen and oxygen atoms, the latter dissolved in the liquid nitrogen as an impurity. A comparative analysis of the in-depth distribution of microhardness in frictionally strengthened surface layers has been performed for the steel with initial structures of tetragonal (untempered) and low-tempered (tempered at 200°C) martensite. A markedly larger depth of strain hardening has been attained upon friction treatment in the quenched untempered steel due to effective development of deformation-induced dynamic aging of high-carbon martensite even at small deformations. It has been established that the strengthening upon deformation of the surface by a sliding indenter exerts a positive influence on the tribological properties (wear rate and friction coefficient) of the steel under the conditions of frictional heating of different intensity.     

The Effect of Surface-Layer Modification of Nickel Alloys on the Heat Resistance of Aluminide Coatings Applied on Gas-Turbine Blades

A method for the preparation of a complex diffusion coating by preliminary saturation of the surface layer of heat-resistant nickel alloys with nickel and by subsequent chrome aluminizing in vacuum using powder mixtures at processing temperatures of 1000 and 1200°C is analyzed. The characteristics of the chemical composition and structure of coatings and comparative data on the heat resistance at temperatures of 1000, 1050, and 1100°C under the conditions of isothermal oxidation are given. It is shown that the complex coating exhibits increased heat resistance owing to an increase in the uniformity of the surface alloy layers obtained by the diffusion nickel plating.     

Influence of Nb Diffusion Layer on Superconductivity of MgB2/Nb/Cu Wires

采用原位法粉末装管工艺(in-situ PIT),以Nb/Cu复合管作为包套材料制备了MgB2超导线材并且在氩气保护气氛中,不同温度条件下保温2h进行成相热处理。分别采用电阻-温度测试、磁矩转变测试、临界传输电流测试以及Nb-MgB2界面磁光研究等分析手段进行研究。结果表明:当热处理温度高于750℃时,在MgB2超导芯丝和Nb阻隔层之间形成一个扩散层,该扩散层的存在阻碍了电流的传输,从而导致在磁测法测试中可以检测到超导相存在,而在传输法测试中无法看到超导传输现象。说明采用Nb作为MgB2超导线带材的扩散阻隔层时其热处理温度不能高于750℃。     

Effect of heating on palygorskite and acid treated palygorskite properties

The behavior of palygorskite as an adsorbent or catalyst support is governed mainly by the magnitude of its surface areas and degree of surface activity. Most heterogeneous catalytic reactions take place at elevated temperatures. It is important and necessary to known the possible changes in the physicochemical properties and hence the catalytic activity due to the thermal treatment. The present work investigates the effect of heat treatment on the surface and textural properties of palygorskite and acid activated palygorskite. Samples were heated at the required temperatures (150°C, 350°C, 550°C and 750°C) for four hours. The chemical analysis, X-ray diffraction, thermal analysis, and textural properties evaluated on the basis of the nitrogen adsorption have been reported for different samples. Acid-treated samples showed a shift of the DTA curves maxima to low temperatures with increasing acid treating time. The weight loss observed between 300–900°C was approximately half of the value observed for the untreated mineral over the same temperature range. On heating, water molecules are removed causing changes in the BET surface area and the porosity. The modification as a function of the temperature differs with the samples. However, at 750°C, a noticeable decrease of the surface area, which is attributed to closure of the mesoporosity, was observed for all the samples. The text was submitted by the authors in English.     

Properties of Nitrogen deep implanted industrial steels

Two types of steels, SKD11 and NAK55, with and without chromium were implanted with 30 keV nitrogen ions to a dose 2 × 10¹⁷ cm² using the new deep implantation process after the preliminary surface treatment by a quasi-neutral intense nitrogen ion flux with the energy 300 eV up to the 10¹⁹ cm². The thickness of the hardened layer significantly increased up to ~ 20 μm by 5 minutes irradiation with 300 eV nitrogen ions at temperatures between 250 and 300°C. The wear resistance of martensitic stee! SKD11 was drastically improved by a factor of 20 after pre-plasma irradiation. Deep implantation also reduces the wear of NAK55 by an order of magnitude, associated with an increase in hardness by a factor of 2.4 at an applied load of 50 gf due to the formation of Fe_2.4N and CrN.     

Determination of Ni Release in NiTi SMA with Surface Modification by Nitrogen Plasma Immersion Ion Implantation

NiTi SMA is a promising material in the biomedical area due to its mechanical properties and biocompatibility. However, the nickel in the alloy may cause allergic and toxic reactions and thus limiting its applications. It was evaluated the influence of surface modification in NiTi SMA by nitrogen plasma immersion ion implantation (varying temperatures, and exposure time as follows: <250 °C/2 h, 290 °C/2 h, and 560 °C/1 h) in the amount of nickel released using immersion test in simulated body fluid. The depth of the nitrogen implanted layer increased as the implantation temperature increased resulting in the decrease of nickel release. The sample implanted in high implantation temperature presented 35% of nickel release reduction compared to reference sample.     

Thermochemical surface treatment of titanium

Abstract

Titanium has very poor tribological properties. Various coatings can be used, for example, TiN, to improve them, but the loading is limited by the low strength of the substrate. Thermochemical treatments produce a layer that is sufficiently thick to support a load, but have to be carried out at high temperatures, 950 and 1050°C, for oxidation and nitriding processes respectively, degrading the core properties. An alternative treatment is desirable that could produce a substantive load bearing layer with good wear properties at 850°C or lower. The obvious candidate species were oxygen, nitrogen and carbon to form hardened diffusion layers, under a thin TiO₂, TiN or TiC surface layer. Nitrogen was not found to be sufficiently active at lower treatment temperature to have any beneficial effects and tended to block the diffusion of other species. Layers formed using various sources of nascent nitrogen, carbon and oxygen were studied. It was found that all the species forming hardened surface layers with the highest values of surface hardness and case depth (72 μm and 922 HV after 24 h at 850°C) were produced using carbon monoxide.     

Impact specimen geometry on T23 and TP347HFG steels behaviour during steam oxidation at harsh conditions

Ferritic T23 steel and austenitic TP347HFG steel have been studied with an emphasis on understanding the impact of specimen geometry on their steam oxidation behaviour. The selected materials were tested over a wide range of temperatures from 600 to 750°C. The tests were carried out in 100% steam conditions for 1000 hours. The tests indicated that the ‘curved-shaped’ specimens show slower mass gain, scale ticking and void nucleation rates than ‘bridge-shaped’ specimens (with flat and convex surfaces combined). Furthermore, a bridge TP347HFG sample showed the formation of lower amount of flaky oxide at 750°C.     

Comparison of the properties of Cu films deposited on four different types of TiN substrates

Cu is now widely accepted as the premier replacement for Al in ULSI interconnect metalliztion. However, it cannot be used without a diffusion barrier since it diffuses through a SiO₂ layer into the Si substrate very easily. TiN is one of the potential candidates for the barrier. In this paper the properties of the Cu films deposited on four different kinds of TiN films were compared. The properties of the CVD-Cu film strongly depend upon the type of the TiN substrate. The Cu film with the highest quality from the viewpoint of surface roughness and thickness uniformity on the four different kinds of the TiN substrate are obtained at 180, 220, 200°C and 200°C for the TiN(TDEAT), TiN(TDEAT+NH₃), TiN(TDMAT), and TiN (sputtered) substrates, respectively. The Cu deposition temperatures at which the Cu films with the lowest electrical resistivity are deposited 200°C on TiN(TDEAT), at 220°C on TiN(TDEAT+NH₃) and TiN(TDEAT) and 180°C on TiN(sputtered), respectively. The smoothest and flattest surface morphology of the Cu film is obtained on TiN(TDMAT), the next on TiN(TDEAT), the third on TiN(sputtered), and the last on TiN(TDEAT+NH₃) as a descending order at the Cu deposition temperatures of 200°C.     

High temperature gas nitriding and tempering in 17Cr-1Ni-0.5C-0.4V steel

High temperature gas nitriding (HTGN) at 1050 °C and tempering of a 17Cr-1Ni-0.5C-0.4V (CNV) steel were experimentally investigated. The phases appearing in the surface layer of the HTGN-treated steel were martensite and austenite with mostly Cr₂N precipitates that were formed by permeated nitrogen, and a small amount of Cr₂₃C₆ and VN precipitates. The reverse migration of carbon hindered the diffusion of nitrogen when nitrogen permeated from the surface to the interior, which resulted in the accumulation of nitrogen on the outermost surface. The strong affinity between nitrogen and chromium atoms induced the diffusion of chromium from the interior to the surface, leading to the substitution of Cr₂₃C₆ for Cr₂N. After tempering the HTGN-treated steel at 500 °C, the dense precipitates of Cr₂N and the increased martensite phase in the surface layer led to secondary hardening, which increased the hardness value up to 901 Hv.     

Microstructure evolution of the Ir-inserted Ni silicides with additional annealing

Thermally-evaporated 10 nm-Ni/1 nm-Ir/(poly)Si structures were fabricated in order to investigate the thermal stability of Ir-inserted nickel silicide after additional annealing. The silicide samples underwent rapid thermal annealing at 300 ° C to 1200 ° C for 40 s, followed by 30 min annealing at the given RTA temperatures. Silicides suitable for the salicide process were formed on the top of the single crystal and polycrystalline silicon substrates, mimicking actives and gates. The sheet resistance was measured using a four-point probe. High resolution x-ray diffraction and Auger depth profiling were used for phase and chemical composition analysis, respectively. Transmission electron microscope and scanning probe microscope were used to determine the cross-section structure and surface roughness. The silicide, which formed on single crystal silicon substrate with surface agglomeration after additional annealing, could defer the transformation of Ni(Ir)Si to Ni(Ir)Si2 and was stable at temperatures up to 1200 °C. Moreover, the silicide thickness doubled. There were no outstanding changes in the silicide thickness on polycrystalline silicon. However, after additional annealing, the silicon-silicide mixing became serious and showed high resistance at temperatures >700 °C. Auger depth profiling confirmed the increased thickness of the silicide layers after additional annealing without a change in composition. For a single crystal silicon substrate, the sheet resistance increased slightly due to the significant increases in surface roughness caused by surface agglomeration after additional annealing. Otherwise, there were almost no changes in surface roughness on the polycrystalline silicon substrate. The Ir-inserted nickel monosilicide was able to maintain a low resistance in a wide temperature range and is considered suitable for the nano-thick silicide process.     

Microstructure Characterization and Corrosion Properties of Nitrocarburized AISI 4140 Low Alloy Steel

Plasma nitrocarburizing treatments of AISI 4140 low alloy steel have been carried out in a gas mixture of 85% N₂-12% H₂-3% CO₂. All treatments were performed for 5 h at a chamber pressure of 4 mbar. Different treatment temperatures varying from 520 to 620 °C have been used to investigate the effect of treatment temperature on the corrosion and hardness properties and also microstructure of the plasma nitrocarburized steel. Scanning electron and optical microscopy, x-ray diffraction, microhardness measurement, and potentiodynamic polarization technique in 3.5% NaCl solution were used to study the treated surfaces. The results revealed that plasma nitrocarburizing at temperatures below 570 °C can readily produce a monophase ε compound layer. The compound layer formed at 620 °C is composed of two sub-layers and is supported by an austenite zone followed by the diffusion layer. The thickest diffusion layer was related to the sample treated at 620 °C. Microhardness results showed a reduction of surface hardness with increasing the treatment temperature from 520 to 620 °C. It has also been found that with increasing treatment temperature from 520 to 545 °C the corrosion resistance increases up to a maximum and then decreases with further increasing treatment temperature from 545 to 620 °C.