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A novel AlCrTiSiN ceramic coating was deposited on 316L austenitic stainless steel (ASS) to enhance its anti-corrosion against 10 vol% HCl solution. Meanwhile, an AlCrN coating was selected for comparison. The results show the AlCrTiSiN consists entirely of single-phase fcc-AlCrTiSiN solid solution, showing nano-multilayered structure. While the AlCrN coating is composed of single-phase fcc-AlCrN solid solution, revealing a typical columnar structure. Growth-related micro-particles (MPs) induce the transformation of growth behavior of the AlCrTiSiN coating over MPs from nano-layered structure to columnar structure, resulting in a reduction in coating densification. Corrosion mechanisms of AlCrTiSiN-coated sample are: pitting corrosion first arrives from surface defects and columnar GBs, and then propagate towards coating subsurface until steel substrate, leading to local corrosion. Subsequently, the galvanic corrosion between coating and substrate happens, resulting in the rapid dissolution of steel substrate beneath the coatings. The combination of pitting corrosion, local corrosion and galvanic corrosion further induces the corrosion cracking, and finally results in coating delamination. In addition, layered interfaces induce the deflection of corrosion cracks along layered interfaces, and further retard the dissolution of coating. Electrochemical and immersion tests confirm that the AlCrTiSiN-coated sample shows a superior corrosion resistance compared with AlCrN-coated one. Superior anti-corrosion of AlCrTiSiN ceramic coating is mainly related to its lower MP number density, denser structure and high-density layered interfaces parallel to coating surface.

Deep cryogenic treatment (DCT) and secondary tempering for 40CrNiMoA steel were carried out to obtain the desirable microstructures corresponding to excellent mechanical properties suiting for the preparation of flex spline of harmonic drive reducer. The effects of DCT and secondary tempering on microstructural characteristics and mechanical properties were investigated by x-ray diffraction, scanning electron microscopy, electron backscattered diffraction and transmission electron microscopy, in association with property measurements. The results show that the DCT promotes the transformation of retained austenite to martensite, the precipitation and homogeneous distribution of carbides as well as the refinement of martensitic substructures. The structural and morphological changes significantly improve the hardness, yield and tensile strength of steels, but slightly lower the elongation of them. Further secondary tempering at special temperatures can successively increase the elongation and fracture toughness of the DCT-treated 40CrNiMoA steels at the cost of slight decrease in hardness and strength due to the reduction in dislocation density. Therefore, the DCT in combination with secondary tempering can improve the comprehensive mechanical properties of 40CrNiMoA steels to produce the flex spline with a higher lifetime.

A multilayered AlCrTiSiN coating, mainly consisting of an inner AlCrN buffer layer and an outermost AlCrTiSiN layer, was deposited on the 316L austenite stainless steel (ASS), and then isochronally annealed at below 900 °C. The effects of microstructures on adhesion strength and corrosion resistance of the AlCrTiSiN coatings annealed at different temperatures were systematically investigated in 3.5 wt% NaCl solution and 10 wt% H2SO4 solution. The results show that the Ti addition notably retards spinodal decomposition of the AlCrTiSiN coating compared with AlCrSiN one. The phase structures of the AlCrTiSiN layer vary from fcc-AlMeN (Me = Cr or/and Ti) solid solution to rich-Me and rich-Al fcc-domains, and then to hcp-AlN, Cr, Cr2N and TiN. Surface defects of the coatings decrease notably with the increasing annealing temperature. Annealing at above 800 °C leads to a notable loss in adhesion strength due to the formation of brittle Cr2N, hcp-AlN and σ-CrFe of the buffer layer. The coatings annealed at 800 °C show the best corrosion resistance in 3.5 wt% NaCl solution, whereas the ones annealed at 700 °C reveals best corrosion resistance in 10 wt% H2SO4 solution.

The strengthening precipitates in a Cu-Ni-P alloy have been investigated using aberration-corrected transmission electron microscope. It is found that coherent plate-shaped particles with hexagonal Ni2P (h- Ni2P) structure are mainly responsible for the hardness of this alloy. The orientation relationship between h-Ni2P precipitates and the matrix should be revised as (111)Cu//(1 2 ¯ 11)h, [1 1 ¯ 0]Cu//[10 1 ¯ 0]h and [11 2 ¯ ]Cu//[1 2 ¯ 1 6 ¯ ]h, and the habit plane of them is parallel to the {111}Cu. Both the morphological and crystallographic characteristics of the h-Ni2P precipitates can be explained by classical theories of phase transformation.

Duplex ceramic coatings, consisting of an inner NiCr-Cr 3 C 2 -based coating and an outmost AlCrN film, were produced on the steel substrate in succession by velocity oxygen-fuel spraying (HVOF) and cathodic vacuum arc methods, and then isochronally annealed at annealing temperatures below 900 °C for 2 h. The thermal stability and mechanical properties of the annealed samples were systematically studied by means of X-ray diffraction, Optical microscope and transmission electron microscope, in association with mechanical property measurements. The results show that the microstructure, phase evolution and mechanical properties of duplex ceramic coatings are significantly dependent on the annealing temperature. Metastable fcc-AlCrN solid solution in AlCrN film first decomposes to rich-Al and rich-Cr domains by spinodal decomposition at 700 °C, leading to a notable increase in hardness due to its smaller grain size and high elastic strain field, and then to equiaxed hcp-AlN and Cr 2 N by the nucleation and growth at 900 °C, leading to a notable decrease in hardness due to the recrystallization and the formation of hcp-AlN. Meanwhile, the both decarburization of Cr 3 C 2 to Cr 7 C 3 occurs at 800 °C, but becomes more intensive at 900 °C, leading to a notable loss in hardness. In addition, the dissolution of Cr 3 C 2 produces high density of porosity, which also reduces the hardness. The hardness tests show the following ordering of load-bearing capacity for the duplex ceramic coatings: 700 °C>As-deposited >800 °C>900 °C. Tribological property measurements demonstrate that the wear resistance of the tested duplex ceramic coatings obeys the following ordering: 700 °C>As-deposited >800 °C>900 °C. The improved wear resistance is due to high surface hardness, load-bearing capacity and thermal stability. In addition, the wear mechanisms are shown.

Coatings are required on mold copper plates to prolong their service life through enhanced hardness, wear resistance, and oxidation resistance. In the present study, NiCr-30 wt.%Cr3C2 ceramic–metallic (cermet) layers were deposited by high velocity oxy-fuel (HVOF) spraying on different designed bond layers, including electroplated Ni, HVOF-sprayed NiCr, and double-decker Ni-NiCr. Annealing was also conducted on the gradient coating (GC) with NiCr bond layer to improve the wear resistance and adhesion strength. Coating microstructure was investigated by scanning electron microscopy and x-ray diffraction analysis. Mechanical properties including microhardness, wear resistance, and adhesion strength of the different coatings were evaluated systematically. The results show that the types of metallic bond layer and annealing process had a significant impact on the mechanical properties of the GCs. The GCs with electroplated Ni bond layer exhibited the highest adhesion strength (about 70 MPa). However, the GC with HVOF-sprayed NiCr bond layer exhibited better wear resistance. The wear resistance and adhesion strength of the coating with NiCr metallic bond layer were enhanced after annealing.

A AlCrTiSiN nanomultilayered coating, mainly consisting of fcc-AlCrTiSiN solid solution and some hcp-clusters at fcc-AlCrTiSiN nanotwin boundaries, was isothermally annealed at 800–1100 °C. Thermal stability and changes in microstructure were studied carefully to illustrate its thermal dissolution mechanism. A thermal induced transformation of hcp to fcc is observed by emission of partial dislocation at hcp/fcc interfaces when annealed at 800 °C. Furthermore, we observe the onset of decomposition of fcc-AlCrTiSiN solid solution to coherently Al-rich and TiCr-rich fcc domains at 1000 °C via spinodal mechanism, accompanied by the precipitation of semi-coherent hcp-clusters within Al-rich fcc sublayers by nucleation mechanism. This transformation results in a notable hardening due to the refinement of grains and the coherency strains caused by spinodal decomposition and the formation of semi-coherent hcp-clusters. Later, annealing at 1100 °C promotes the dissolution of layered structures by pinching off of hcp sublayers, the transformation of fcc-AlCrTiSiN solid solution to Cr, Cr2N and hcp-AlN particles and the coarsening of hcp-AlN particles, resulting in a notable loss in hardness.

Advanced AlCrSiN and AlTiSiN coatings were deposited on high-speed steel by cathodic vacuum arc. The microstructures, mechanical and tribological properties were studied, as well as cutting performance. The results show that multilayered AlCrSiN coating mainly consists of nanocrystalline fcc-AlCrN and a few amorphous Si3N4 phases, with an average module period of about 6.0 nm. While the AlTiSiN coating reveals nano-composite structure consisted of nanocrystalline fcc-AlTiN and hcp-AlN embedded into Si3N4 amorphous matrix. The AlCrSiN-coated tool reveals a more excellent cutting performance when compared with the AlTiSiN-coated tool due to its higher hardness, adhesion strength, H3/E*2 ratio and wear resistance when compared with the AlTiSiN coating.

The corrosion behaviors in 10 wt% H2SO4 solution of the Al Ti Si N coatings, deposited on 316L stainless steel using multi-arc ion plating then vacuum annealed at 700 °C, 800 °C and 900 °C for 2 h, was investigated. The microstructures, compositions and surface morphologies of the coatings were characterized by utilizing X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscope (XPS) and scanning electron microscope (SEM) analyses. The adhesion strength and corrosion behavior of coatings were measured by scratch test and electrochemical polarization curves, respectively. The results indicated that the as-deposited coatings were mainly comprised of solid solution (Ti,Al)N phase and amorphous Si3N4 phase. With increasing annealing temperature, the solid solution gradually decomposed into fcc-TiN and fcc-AlN phases and further into hcp-AlN phase. The defects on coating surface and adhesion strength of coatings were improved simultaneously. The electrochemical results revealed that all coated samples had better corrosion resistance than the substrate, and the coatings annealed at 800 °C exhibited the best corrosion behavior in acid solutions. This was caused by the formation of amorphous Si3N4 phase and anti-corrosion hcp-AlN phase.

Advanced HVOF-PVD duplex coatings were produced on the medium carbon steel by combinations of High Velocity Oxygen-Fuel (HVOF) and arc ion plating. The microstructures and mechanical properties were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) in association with mechanical property measurement. The results show that the duplex coating are composed of an inner NiCr-Cr 3 C 2 -based HVOF-sprayed layer mainly consisted of γ-NiCr and Cr 3 C 2 phases, and an outmost PVD-AlCrN layer containing fcc-AlCrN phase. Duplex coatings reveal more excellent wear resistance when compared to the HVOF-sprayed coating. The improved wear resistance is mainly related to the outmost AlCrN layer with more excellent wear resistance in comparison to the HVOF-sprayed coating against WC ball. The AlCrN layer deposited on NiCr-75 wt.% Cr 3 C 2 duplex coating reveals higher wear resistance than that of the AlCrN layer deposited NiCr-30 wt.% Cr 3 C 2 duplex coating. The improvement of wear resistance is mainly associated to its higher surface hardness, load capacity and bond strength. The main wear mechanisms of the duplex coatings are adhesive and oxidation wear, whereas the ones of the single HVOF-sprayed NiCr-Cr 3 C 2 -based coating are adhesive wear as well as spalling and chipping wear.

AlCrN coatings were deposited on 316L stainless steel by multi-arc ion plating. The phase structures were controlled and optimised by vacuum annealing at 700 °C, 800 °C, and 900 °C, each for 2 h. The microstructures and morphologies of these coatings were examined by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscope, in association with adhesion strength measurement, residual stress measurement and potentiodynamic polarisation with 3.5% NaCl and 10% H2SO4 solutions. Results show that the solid solution hcp-(Cr, Al)N phase of as-deposited AlCrN coatings decomposes into hcp-AlN and CrN phases, then further decompose into N and Cr with increasing annealing temperature. Metal particles and droplets on the coating surface were gradually removed simultaneously when compared with as-deposited coatings. The highest adhesion strength was obtained after annealing at 700 °C. It decreased with increasing annealing temperature due to the σ-FeCr phase and Cr2N phases, and the residual stress decreasing. The potentiodynamic polarisation measurements showed that the corrosion resistance of such coatings was significantly improved after annealing: the coatings annealed at 800 °C showed the best protective efficiency because some corrosion resistance phases (h-AlN, Al2O3, CrN, and Cr2N) were generated.

The chromized layer on carbon steels demonstrates high hardness and excellent wear-resistance. However, it usually suffers from its thin thickness and the softened underneath diffusion layer owing to the decarburization of the diffusion layer. In the present work, a double strengthened surface with a chromized layer and a N/C-rich diffusion layer was fabricated on a carbon steel by a nitro-chromizing process. The effect of chromizing time and cooling method on the microstructure and property of the nitro-chromized surface layers was investigated. The phase transformations occurring in the double strengthened surface were also studied in detail. Although it is difficult to improve the chromized layer, which consists of CrN, β-Cr2N and (Cr,Fe)7C3 phases, the microstructure of the diffusion layer with a thickness of more than 500 μm can be optimized to contain ultrafine martensite–bainite associated with nanometer-sized precipitates and retained austenite, leading to surface hardness of ~ 1000 HV or higher. The microstructure in the diffusion layer plays a key role in improving the property of the double strengthened surface.

Four microalloyed samples were designed to study the effects of Ti and B additions on microstructures and mechanical properties. Experimental results show that the samples without B addition mainly contain well-developed pearlite and polygonal ferrite, whereas the B-containing samples consist of degenerated pearlite, polygonal ferrite, and Widmanstatten ferrite (WF). The B addition promotes the precipitation of the complex (Ti,Al,Nb)N and (Ti,Al,Nb)2CS phases during the hot-rolling process. Grain sizes are significantly refined by the combinations of undissolved (Ti,Al)N, (Ti,Al,Nb)N complex, (Ti,Al,Nb)2CS, and fine inclusions, which act as the nucleation sites of intragranular ferrite. The core of complex (Ti,Al,Nb)N precipitate is undissolved Ti-N-rich (Ti,Al)N phase, and the cap is Nb-N-rich (Nb,Ti)N phase. The property measurements show that the B addition enhances comprehensive properties of tensile strength and elongation, but decreases fracture toughness due to higher contents of the WF and subgrains.

The corrosion behaviors in 3.5% NaCl and 10% H2SO4 solutions of the nano-composite Al-Cr-Si-N coatings, deposited on stainless steel 316L substrates using multi-arc ion plating process, annealed at 700 °C, 800 °C and 900 °C, each for 2 h, was studied. The phase structures, surface morphologies, adhesion strength, and corrosion properties of the Al-Cr-Si-N coatings before and after vacuum annealing were investigated. Results indicated that, with increasing annealing temperature, the phase structures of the nano-composite Al-Cr-Si-N coatings varied from solid solution (Cr,Al)N phase to CrN, Cr2N and AlN phases with a hexagonal close packed structure (hcp-AlN), and then to CrN, Cr2N, hcp-AlN and Cr phases, and finally to CrN, Cr2N, hcp-AlN, Cr and σ-FeCr phases. The defects on the coating surface were decreased simultaneously. The samples annealed at 800 °C had the highest adhesion strength. The potentiodynamic polarisation measurements showed that the corrosion resistance of coatings was improved after annealing. The coatings annealed at 800 °C had the best corrosion resistance in 3.5% NaCl solution, and the coatings annealed at 700 °C had the best corrosion resistance in 10% H2SO4 solution.

The AlCrN, CrBN and AlCrBN coatings were deposited on Ti6Al4V alloy by cathodic vacuum arc with powder-metallurgical targets. The phase structures, surface and cross-sectional microstructures, mechanical and tribological properties of these coated samples were comparatively studied. The results show that the B-containing coatings consist of fcc solid solution embedded into a-BN/CrB amorphous phases, whereas the AlCrN coating is composed of single-phase fcc-AlCrN solid solution. The preferred orientation is changed from (111) plane in CrBN coating to the (200) plane in the AlCrBN coating. As a result of complex effects of B-induced fine-grained strengthening and the Al/B solution strengthening, the AlCrBN coating shows the highest hardness and the best plastic deformation resistance. The results of wear tests reveal that all PVD coated samples show the better tribological properties compared to the uncoated Ti6Al4V alloy, and the highest wear resistance is observed in the AlCrBN coated sample. The main wear mechanism for coated samples is oxidation wear, whereas the one for the uncoated Ti6Al4V alloy is abrasive wear.

AlCrN/TiSiN nanomultilayer coatings, basically consisting of single-phase fcc-AlCrTiSiN solid solution, were prepared by co-deposition method with Al30Cr70 and Ti72Si18 targets. With substrate negative bias voltage increase from 50 V to 110 V, the hardness of nanomulitlayer coatings is increased from 32.1 GPa to 36.5 GPa, and the growth behavior changes from (2 0 0)fcc preferred orientation to coexistence of both (2 0 0)fcc and (1 1 1)fcc preferred orientation. Low interfacial energy supports the epitaxial growth, resulting in an increase in strain energy of coating systems due to the lattice misfit between neighboring sublayers. Increased strain energy is overcompensated by the formation of interfacial dislocations and dislocation loops as well as fcc-AlCrTiSiN nano-twins and hcp-AlN clusters at twin boundaries. Additionally, the Cr-ion etching induces to form a thin amorphous loose layer (LL) between coating and steel substrate during the pretreatment process. High substrate bias voltage promotes the transformation of amorphous phase to the (Cr,Fe)N solid solution during the coating deposition process, resulting in a notable increase in adhesion strength.

AlCrN coating which has been widely applied in industrial application was produced on the surface of nitrocarburized SKD 11 cool-work tool steel by physical vapor deposition (PVD) method. The effects of nitrocarburizing pretreatment and PVD deposition temperature on microstructures, mechanical and tribological properties of the coatings were investigated. The results show that the AlCrN coating consists of an inner CrN adhesion layer with columnar growth and an outmost AlCrN work layer with planar growth, and the AlCrN coating shows a superior hardness of about 43 GPa. The nitrocarburizing pretreatment considerably improve adhesion strength, load capacity and wear resistance of duplex coated samples when compared with the single AlCrN coated samples. The improved mechanical and tribological properties are mainly related to the thicker nitrocarburizing layer and the gradient in the hardness profile of the duplex coating. In addition, the nitrocarburizing-PVD AlCrN duplex coated samples can be further enhanced by increasing deposition temperature of PVD coatings. The main wear mechanisms of duplex coated samples are oxidation wear or oxidation wear and adhesion wear, whereas the main wear mechanisms of single AlCrN coated samples are spalling and chipping wear as well as oxidation wear.

In the present work, AlCrN coating and AlCrSiN multilayer and nanocomposite coating were designed and deposited on the surface of high speed steel (HSS) cutters. The microstructures of these coatings were investigated systematically by means of grazing incidence X-ray diffraction (GIXRD), X-ray photoelectron spectroscope (XPS), electron probe X-ray microanalysis (EPMA), scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM), in association with mechanical property measurement and corresponding cutting test. The results showed that the AlCrN coating mainly composed of nanocrystalline fcc-CrN, hcp-AlN and fcc-(Cr,Al)N solid-solution. In addition to these nanocrystalline phases, a few amorphous Si 3 N 4 phases were observed for the AlCrSiN multilayers and nanocomposite coating with a stronger {2 0 0} preferred orientation. The modulation period (6 nm) of the AlCrSiN coating was much smaller than that of the AlCrN coating (18 nm). The service life of the AlCrSiN coated tool increased approximately 40% longer in comparison with the AlCrN coated tool because of its more excellent mechanical properties (48 GPa hardness, 1123 MPa toughness, 52 N LC2 adhesion strength and 0.25 average friction coefficient). During the cutting process, the wear mechanisms of coated tools at the early stage and mid-stage were abrasion wear and adhesion wear, respectively. And the worn loss of AlCrSiN coated tool was less than that of AlCrN coated tool.

In the present work, based on AlCrN coatings, AlTiSiN and AlCrTiSiN multilayer and nanocomposite coatings were designed and deposited on high-speed steel (HSS) specimens and cutters by cathodic vacuum arc process. The microstructures of these coatings were investigated by grazing incidence X-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and high-resolution transmission electron microscope (HRTEM), in association with mechanical property characterisation, and also with a cutting test used to check the service life of coated tools. The results showed that the AlTiSiN coating was composed of nanocrystalline TiN and hcp-AlN. The AlCrTiSiN multilayers and nanocomposite coating contained (111), (200), and (220) planes of TiN and CrN with a face-centred cubic structure (fcc) and nanocrystalline fcc-(Cr,Al)N phases. The AlCrTiSiN coating had a stronger diffraction (200) peak compared with the AlTiSiN coating. Those coatings were superlattice with nanocomposite structures containing nanocrystalline and amorphous phases. The modulation period (7 nm) of the AlCrTiSiN coating was much smaller than the 12 nm of AlTiSiN. A special Cr2N particulate phase existed in the AlCrTiSiN coating. The service life of an AlCrTiSiN coated tool increased by approximately 50% when compared with that with an AlCrN coating because of its excellent mechanical properties (41.14 GPa hardness, 1.07 GPa toughness, 60 N LC2 adhesion strength, 0.2 average friction coefficient, and 36.5 nm (Ra) roughness).

Duplex-treated composite ceramic coatings with and without compound layer were produced by the combination of plasma nitrocarburizing and follow-up multi-arc ion plating. The microstructures and mechanical properties of the ceramic coatings were investigated by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy, in association with property characterization. The results show that the composite ceramic coatings are composed of an inner nitrocarburized layer, a CrN interlayer and an outmost AlCrTiSiN layer. The AlCrTiSiN layer consists mainly of alternately nanoscaled (Cr,Al)N sublayer and amorphous sublayer with a few (Ti,Al)N phases embedded in a matrix of amorphous Si 3 N 4 and Si. The compound layer has transformed to the γ′-phase sublayer, which enhances considerably the adhesion strength of the CrN interlayer to compound layer. The improved adhesion strength is attributed to the γ′-phase acting as nucleation sites of epitaxial growth for the CrN phase. The composite ceramic coating with compound layer reveals much higher hardness, bearing capacity and wear resistance when compared with the composite ceramic coating without compound layer. The improvement of mechanical and tribological properties is associated with presence of the γ′-phase sublayer, which provides a smooth transition, gradient in hardness and stress between the substrate and the CrN/AlCrTiSiN coating. In addition, the hard γ′-phase sublayer provides a strong supporting effect for CrN/AlCrTiSiN layer under loading.

The AlCrN and AlCrTiSiN coatings were produced on the surface of plasma nitrocarburized T10 steels by multi-arc ion plating. The comparison of the microstructures and mechanical properties of the duplex coatings were investigated by means of X-ray diffraction, optical microscope, scanning electron microscope and transmission electron microscope, in association with mechanical property measurement. The results show that the AlCrN coatings with columnar grown are mainly composed of nanocrytalline fcc-(Cr,Al)N phases with {111} preferred orientation, whereas the superlattice and nanocomposite AlCrTiSiN coatings with planar growth mainly consist of nanocrystalline fcc-(Cr,Al)N phases with {100} perfected orientation, hcp-AlN and Si3N4 amorphous phases. The AlCrTiSiN duplex coating with the compound layer reveals higher hardness, adhesion strength, load capacity and lower friction coefficient when compared with the other duplex coatings, which is due to its superlattice and nanocomposite structure. Additionally, these improved properties are related to the appearance of the γ′-phase which plays the nucleation sites for the coating nitrides and provides a strong supporting effect for the AlCrN and AlCrTiSiN coatings. The main wear mechanism of the duplex coatings without compound layer is spalling and chipping wear as well as tribooxidation wear, whereas the main wear mechanism of the duplex coatings with compound layer is tribooxidation wear.

Superhard CrAlN/TiAlSiN nano-multilayers deposited at various substrate bias voltages were produced on the surface of Si (100) wafers and high-speed steels by cathodic vacuum arc. The microstructures of these coatings were investigated systematically by X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM), in association with mechanical property characterization. The HRTEM observation shows that these coatings have a nano-multilayer structure containing alternatively fcc-(Cr,Al)N sublayer and amorphous sublayer with some nanocrystalline fcc-(Ti,Al)N phases embedded in this amorphous matrix. The coherent epitaxial growth structure is observed along the {100} crystal plane of the fcc-(Cr,Al)N phase and the {100} crystal plane of the fcc-(Ti,Al)N phase. The orientation relationship between them is as follows: {100}(Cr,Al)N//{100}(Ti,Al)N and [001](Cr,Al)N//[001](Ti,Al)N. Mechanical property characterization shows that the coating hardness is dependent on the substrate bias voltages, and the friction coefficients of these coatings with a higher substrate bias voltage are found to be much lower than those of the coatings deposited at a lower substrate bias voltage. The improvement of the friction coefficient is attributed mainly to the formation of tribochemical reaction films. In addition, the much lower friction coefficient can also be related to the higher hardness and fracture toughness.

The present work aimed to improve the wear resistance of titanium carbonitride (TiCN) films by the solid solution of aluminium atoms forming aluminium–TiCN films with varying Al/Ti atomic ratios, which was deposited by arc ion plating technique with a gas mixture of Ar, N2 and C2H2. The wear rate of the films was investigated by a Pin-On-Disc wear tester at room temperature (RT) and 600°C. The results indicated that the aluminium addition induced the increase in wear rate at RT. However, the Al introduced films showed good antifriction effect at 600°C, possessing lower wear rate than TiCN films, and their antiwear property was continuously improved with further increasing the Al/Ti atomic ratio. The mechanism of wear was discussed considering the temperature and oxygenic factors.

The coarsened grain boundaries (GBs) with vein-like morphology frequently appear in the nitrogen diffusion layer of nitrocarburized carbon steels. The electron probe X-ray microanalysis shows that such vein-like GBs are rich in nitrogen and carbon atoms. Transmission electron microscopy and scanning electron microscopy further reveal that the coarsened GBs consist of γ′-nitrocarbide (Fe4(C,N)) and e-nitrocarbide lamellas that are formed during nitrocarburizing due to high nitrogen concentration at GBs. It is shown that many of {111} micro twins exist in the γ′-phase lamellas and thin e-phase slices prefer to nucleate at their twin boundaries with the orientation relationship of {0001}e//{111}γ′. Upon growing large γ′-lamellas may become faceted and thin e-lamellas may grow thicker and become the main portions in the vein-like GBs. The microstructure evolution occurring in the vein-like GBs can be depicted as: α + [N]/[C] → γ′ + [C,N] → e-nitrocarbides.

Ferritic nitrocarburizing is a widely employed industry process by which a strengthened nitrocarburized surface can be formed on mechanical tools or parts made of steels. Mainly composed of the e-Fe2–3(C, N) and γ′-Fe4(C, N) carbonitride phases as well as the α-Fe phase, the nitrocarburized surface has featured microstructures and properties that are directly related to the phase transformations occurring in the surface layers. Thus far, the following phase transformation sequence for the surface has generally been accepted: α-Fe + N/C → e → γ′. In the present work, these phase transformations were systematically revisited by microstructure and property characterizations in association with a controlled nitrocarburizing process by which the microstructures and properties of the surface are adjustable. Our study demonstrates that, to fully understand the microstructure and the property of a nitrocarburized surface, it is necessary to adopt the phase transformation sequence α-Fe + N/C → γ-N/C + N/C → γ′ + N/C → e, in which the existence of a transitional austenite phase containing N/C atoms (γ-N/C) must be assumed and the γ′ phase actually forms prior to the e phase.