Compound Coatings Research Articles

Surface Engineering with Light Alloys - Hard Coatings, Thin Films, and Plasma Nitriding

Light alloys have been attracting increasing attention over the past decade, since they can be used to reduce weight and save energy. For many years, light metals such as titanium and aluminum have also been used to synthesize hard compound coatings such as physically vapor deposited (PVD) TiN, (Ti,Al)N, and chemically vapor deposited (CVD) Al2O3. The coatings field is developing rapidly. Combining plasma-aided coating and diffusion processes has led to the development of so-called “duplex treatment,” consisting of plasma nitriding and subsequent hard coating. Another interesting development is TiN coating of aluminum vacuum parts, such as pumps, to reduce degassing and make the cleaning of the surfaces easier. Despite the many advantageous properties of light alloys, their surface properties sometimes cause problems. For example, galling may be a severe problem with titanium parts, and plasma nitriding has been applied successfully to combat it. However, due to adherent oxide scale, plasma nitriding of aluminum has proven to be more difficult. In this paper, we discuss some recent trends in the application of plasma-aided coating, thin film deposition, and diffusion processes, and give practical examples of industrial applications.

622 プラズマ粉体肉盛法によるNiTi金属間化合物層の形成と摩耗特性(OS コーティング・溶射)

In this work, feasibility study has been conducted to produce NiTi intermetallic compound coatings using both composite powder of NiTi (alloyed powder) and physically mixed powder of Ni and Ti by plasma transferred arc welding process. Wear characteristics of the coatings were evaluated by a modified Okoshi-type wear tester. Based on the obtained results, it was possible to produce intermetallic compound coatings on carbon steel from the simply mixed powder as well as composite powder by plasma transferred arc welding process. Hardness value reached up to 800HV in the NiTi coatings, and then the resistance to sliding wear was much improved in comparison with that of Stellite#6 coatings.

Cavitation erosion mechanism of NiTi coatings made by laser plasma hybrid spraying

NiTi intermetallic compound is known to be a high cavitation erosion-resistant material. The erosion behaviors of NiTi intermetallic compound coatings made by laser plasma hybrid spraying (LPHS) were studied. The erosion resistance of the NiTi coatings depended strongly on the chemical composition of the coatings and the laser irradiation condition, because the NiTi phase and the microstructure of the coatings were varied by those conditions. The best erosion-resistant coatings were obtained with the conditions of nickel composition richer than that of equiatomic NiTi and irradiated laser power density greater than 6×10 8 W/m 2. The cavitation erosion resistance of the coating was about 380-fold that of a titanium alloy substrate. High erosion resistance of these coatings was obtained due to a combination of two factors, namely, super elasticity due to austenite-phase NiTi and high work hardenability due to excess soluble Ni.

レーザー複合溶射法による耐エロージョンＮｉＴｉ皮膜の作製

The intermetallic compound coating made by a laser and plasma hybrid spraying has been studied. The laser plasmahybrid spraying system (LPHS) was constructed with a 5 kW CO2, laser and a low pressure plasma spraying equipment. In this system, the plasma sprayed layer was rapidly remelted and solidified by the CO2 laser irradiation. It is possible to synthesize intermetallic compound coatings from the simply mixed powder using this system. To improve the cavitation erosion resistant of Ti-alloy, a NiTi coating on the Ti-alloy is investigated. The NiTi intermetallic compound is known as an erosion resistance material. In a case of only plasma spraying process, Ti and Ni particle were separated mutually in the coatings, but by the laser plasma hybrid spraying, Ni-Ti intermetallic compound was formed in the coating. And the coating was joined metallurgically with substrate and contained few defects. The ratio of phases, such as NiTi, NiTi2 and Ni3Ti was varied with the laser irradiation conditions and powder mixed ratio.To evaluate the erosion resistance of coatings, vibratory cavitation erosion was evaluated. The cavitation erosion resistance of the coatings was about 70 times as much as Ti-6Al-4V substrate.

The shear impact wear behavior of Ti compound coatings

The failure behavior of Ti compound coatings was evaluated under normal and shear impact conditions at room and elevated temperatures. Monolayers and combined multilayers of TiAlN and TiAlCN were deposited onto high speed steel by a cathodic arc ion plating process. The shear impact loading mode was obtained by rotating the coated disk specimen at a speed of 0.8 m s −1 under repetitive normal impact loading of 10 N using a CoWC ball indentor with a frequency of 5 Hz. The impact resistance under normal impact loading appeared to be higher in the order TiAlN, TiAlN/TiAlCN and TiAlCN in accordance with the adhesive strength measured by HRC indentation tests. Meanwhile the addition of shear force during repetitive normal impact loading by specimen rotation reduced significantly the failure resistance of all the films, both at room temperature and 600°C, with a change in failure mode. It was observed through progressive failure analysis with increasing repetitive loading cycles that the failure under shear impact loading was accelerated owing to the promotion of crack formation as well as laminated fragmentation by increasing tensile and shear stresses at the ball trailing zone resulting from tracking forces during repetitive instantaneous impacting and sliding. The propensity for failure became more severe owing to substrate softening for all the coatings as the temperature increased to 600°C.

Incorporation of Milk Fat and Milk Fat Fractions into Compound Coatings Made from Palm Kernel Oil

The potential of incorporating anhydrous milk fat and milk fat fractions into compound coatings based on palm kernel oil was investigated. Fractionation of milk fat by melt crystallization was utilized to prepare five fractions with different melting profiles. The anhydrous milk fat and milk fat fractions were added at 5, 10, and 15% of the fat phase in compound coatings made with palm kernel oil. Fats were analyzed for fatty acid and triacylglycerol profiles, solid fat content, thermal profile, and melting point. Coatings that were made with the addition of anhydrous milk fat or milk fat fractions were generally softer than the control coating, although hardness depended on the melting point of the added milk fat fraction. Coatings made with fractionated, hydrogenated palm kernel oil developed fat bloom (the whitish haze that forms on a chocolate surface) faster than coatings made with fractionated palm kernel oil during storage at ambient conditions. As hardness increased, induction time for bloom formation and time to full bloom decreased. Binary mixtures of palm kernel oil and milk fat exhibited diluent mixing effects and contained only β’ polymorph crystals.

Mixtures of palm kernel oil with cocoa butter and milk fat in compound coatings

AbstractThermal behavior of binary mixtures of palm kernel oil (PKO), cocoa butter (CB), and anhydrous milk fat was used to study mixed‐lipid crystallization. This study was related to the physical properties of compound coatings made with these fats. Phase behavior was studied by evaluating changes in melting behavior with composition and time, by creating isosolid diagrams, and by monitoring polymorphic behavior. For binary mixtures, multiple melting peaks and eutectic formation were observed for 30–50% addition levels of CB to PKO, but not for addition of milk fat to PKO. For compound coatings and binary mixtures, made with the same fat composition, hardness of compound coatings increased as solid fat content (SFC) at 25°C of binary mixtures increased. Also, as SFC at 25°C of the binary mixtures increased, induction time for bloom formation and time to fully bloom for compound coatings decreased. Observation of eutectic behavior for binary mixtures indicated softness in a compound coating with the same fat composition, but the converse was not necessarily true.

めっき，塗装材のはく離技術 チタン系イオンプレーティング皮膜のはく離

めっき，塗装材のはく離技術 チタン系イオンプレーティング皮膜のはく離

Applications of milk‐fat fractions in confectionery products

AbstractIncompatibilities between fats limit the use of modified milk fat in confectionery applications. To further enhance the use of milk‐fat fractions in chocolates and compound coatings, a better understanding of mixed crystallization effects between lipids is required. Recent work documents that highmelting fractions incorporated into chocolates drastically reduce bloom formation and cause less softening than anhydrous milk fat. Isosolids diagrams for mixtures of cocoa butter and milk‐fat fractions show that softening occurs due to both dilution effects and a slight eutectic formation. Incorporation of milk‐fat fractions into palm kernel oil‐based coatings shows some differences with results in chocolates. Milk fat and its fractions cause significant bloom formation in these coatings, as compared to the control, and cause significant softening. However, both milk fat and milk‐fat fractions are fully compatible with palm kernel oil, based on isosolids diagrams. Softening occurs only because of dilution effects, rather than eutectic formation. Further work is necessary to understand the effects of milk‐fat fractions on bloom formation in compound coatings.

Factors affecting growth defect formation in cathodic arc evaporated coatings

The origin of the conical features on the surfaces of arc evaporated hard compound coatings was investigated. A simple metallographic technique was employed to show that these conical features are growth defects made of the coating material (TiN in our case) precipitated by macroparticles of the cathode material, and not the macroparticles themselves. The effect of bias voltage characteristics, such as the amplitude (for d.c. voltage), frequency and duty cycle (for pulsed voltage), on the evolution of defects was also investigated. An increase in the amplitude or duty cycle resulted in a decrease in the defect density, R a and the surface area covered with the defects. A simple explanation for the phenomena observed is suggested.

Production of duplex coatings by thermal spraying and nitriding

Limitations of surface treatments can be apparent under the complex loading experienced by engineering parts and components. These limitations can be removed by using duplex techniques. The process combination of thermal spraying and nitriding makes it possible to produce coatings with increased resistance for applications involving complex stress and loading conditions. The interactions between thermal spraying and nitriding have been investigated and both processes optimised to achieve improved properties of the compound coatings. Metallographic, X-ray, wear, and corrosion test results for the compound coatings are presented.

Production of duplex coatings by thermal spraying and nitriding

Limitations of surface treatments can be apparent under the complex loading experienced by engineering parts and components. These limitations can be removed by using duplex techniques. The process combination of thermal spraying and nitriding makes it possible to produce coatings with increased resistance for applications involving complex stress and loading conditions. The interactions between thermal spraying and nitriding have been investigated and both processes optimised to achieve improved properties of the compound coatings. Metallographic, X-ray, wear, and corrosion test results for the compound coatings are presented.

Ｎｉ‐Ａｌ系メカニカルアロイ粉末のＤＣプラズマ溶射による金属間化合物皮膜の作製

Experimental conditions for the fabrication of intermetallic compound coatings by DC plasma spraying of Ni/Al mechanically alloyed powders have been investigated.The results obtained are summarized as follows ;(1) In atmospheric plasma spraying, APS, the obtained coating was composed of two or more phases : Ni-rich phase, and Alrich phase. Ni/Al MA powder seemed to be subjected to phase separation during plasma spraying. On the other hand, homogeneous intermetallic coatings were obtained by low pressure plasma spraying, LPPS, due to the diffusion of two element in the sprayed powders.(2) The dominating factor for phase separation for MA powders during plasma spraying seemed to be the heat flow from surrounding plasma ; the contributions of other factors, such as, mixing of the powder, composition of working gas, oxidation of the powder and acceleration force in plasma flame, were negligible.(3) By low pressure plasma spraying or HVOF spraying of MA powder, the intermetallic coating can be fabricated easily. Even in the APS process, intermetallic coating can be obtained by the spraying of sizeable MA powder.

Failure characterization of tools coated with hard compound coatings

A coating process is usually the last step in the macufacture of many devices used throughout industry. Hard compound coatings such as titanium nitride and chromium nitride have found their use in the area of wear and abrasion resistance. Superior mechanical and chemical coating properties will not protect a tool or component from failing if the substrate material exhibits flawed metallurgy or poor surface finish. In addition, improper substrate cleaning, conditioning or coating application could also be the reason behind the failure. Techniques, such as metallography, electron microscopy, energy-dispersive X-ray spectroscopy, microhardness and adhesion testing may be used to characterize different types of failure. This work presents an approach to failure analysis of coated devices, which is demonstrated in several case studies.

Fire, climate, and the persistence of desert varnish near Dampier, Western Australia

In the semi-arid region near Dampier, discontinuous black and dark red coatings (desert varnish) have developed mainly on outcrops of granophyre. Coatings which have persisted occur on the most stable surfaces of large, rather than small, boulders. Rock coatings are absent both from fire-affected outcrop margins and around sediment patches within boulder slopes, and from the spray zone on the coastal margin. Sea level rise between about 17,000 and 6000 yr B.P. would have produced a landward-migrating spray zone within which salt weathering probably destroyed varnish before inundation. The remaining rock coatings have variable chemistry, and include compound coatings with superimpositions of thin Fe-rich, thicker SiAlMnFe layers, and an upper coat of SiAlFe, indicating fluctuatinng environments. Within major outcrops, the best-developed coatings occur on large and stable boulders beyond the reach of fire and salt spray, and often in summit or mid-slope positions. Much varnish loss can be attributed to factors other than climatic change, with coatings presently forming at a slower rate than they are being destroyed.

Orientation relationship between Γ phase and α–Fe in commercial galvanneal steel coating

The steel coatings' forming technology and their resulting mechanical performance are of primary concern to the automobile and appliance industries, for they determine directly the long-term structural integrity of the final products. In automobile industry, steel coating plays a crucial role for extended warranty of their product. The recent trend in coatings is an increase in galvannealed coatings.The iron-zinc compound coatings produced by galvannealing bring about a dramatic improvement, in terms of coating performance, compared to pure zinc coatings. The improvement includes corrosion resistance, weldability and paintability in addition to energy and material efficiency. However, there is still one serious obstacle which prevents the industry-wide use of galvannealing as the dominant steel coating technology: Its powdering and flaking tendency during press forming processes. There are a number of empirical hypotheses which propose that the presence of various Fe-Zn intermetallic phases influences the powdering/flaking tendency of galvannealed coatings. Nevertheless, not enough microstructural information is available except those obtained by SEM and X-ray diffraction.

A comparison of IBAD films for wear and corrosion protection with other PVD coatings

Ion beam assisted deposition is presently introduced into fabrication processes in industry. Now the question arises which are the advantages and disadvantages of IBAD in comparison with other PVD-techniques and where its application potential is. In this paper results of comparative studies of IBAD and methods such as sputtering and ion plating are discussed. The subjects are medium energy ion beam assisted deposition and films for wear and corrosion protection. As a general result it turns out that IBAD films show superior performance when low process temperatures are required, as it is the case for special heat treated steels and aluminium alloys. In these cases, both elemental IBAD coatings such as Al and compound coatings such as TiN are able to offer a better protection against corrosion, partially also wear, than most of the other PVD techniques. The reasons for this observation are higher structural density and adhesion of the IBAD films. The required film growth conditions, mainly energy input, are provided by highly energetic ions while the bulk of the substrate can essentially be kept at low temperature.

Chemical Metallurgy in the Vapor Phase

Abstract Most of this century, chemical metallurgy has been associated with extractive and refining processes involving primarily metal and slag (oxide, fluoride, etc. ) phases in the liquid state. In the past 20 years, a new dimension to chemical metallurgy has come up involving the vapor phase, via processes such as chemical vapor deposition, physical vapor deposition and their derivatives This paper deals with the vapor phase chemical metallurgy processes and the various materials that can be derived. For example, carbide, nitride, oxide and other refractory compound coatings with controlled stoichiometry can be produced. This has resulted in many new applications in tribology, optics, microelectronics and related disciplines. The latest developments involve coating of metastable materials like cubic boron nitride, diamond, i-carbon, etc.

The effects of precoating and bias voltage on the adhesion of reactive arc evaporated TiN and ZrN coatings

The effects of precoating and bias voltage on adhesion have been studied for reactive arc evaporated TiN and ZrN coatings on high speed steel. Pure Ni, Ti, and Zr interlayers were precoated as single or double layers with different thicknesses prior to the deposition of the compound coatings. The adhesion was evaluated by comparing acoustic signals through the scratch test method with incremental applied load. Precoating with a double layer significantly enhanced the adhesion of both TiN and ZrN coatings. A single interlayer precoating also produced an effective improvement of adhesion. The improvement was more pronounced for thicker single interlayers of Ti and Ni in TiN coating. Adhesion was also improved with increasing negative bias voltage for TiN coating without interlayer precoating. The mechanism for the improvement of adhesion by precoating is proposed to be stress accommodation in the interlayer.

The influence of the composition and coating parameters of PVD Ti-Al-V(C.N) films on abrasive and adhesive wear of coated cemented carbides

This paper reports on the development of hard materials in the quaternary Ti-Al-V(C,N) system using magnetron sputter ion plating. All investigated compound coatings crystallized in a cubic face-centred TiN lattice with reduced or enlarged lattice parameters, depending on the amount and radius of foreign atoms. Microstructural, X-ray diffraction, microprobe and micrographic analyses were used to confirm the composition of the hard coatings and to demonstrate the phases occurring. Annealing tests up to 1000 °C give evidence of the stability of these metastable phases. Properties of the coatings on cemented carbide cutting inserts have been determined by metallographic examinations such as film thickness measurements, microhardness, hot microhardness and scratch testing to estimate film adhesion. The influence of aluminium and vanadium, in a titanium-based hard coating, on the flank wear and the crater wear is described. It was shown that the addition of vanadium increases the resistance to cratering but tends to increase the brittleness of the material manifested in flank wear. The influence of aluminium on flank wear and ductility was also demonstrated. In addition, in the reactive mode, the stoichiometry of these hard phases is varied during the deposition process by using nitrogen and methane to produce carbonitrides.