ZrO2对激光烧结Al2O3/SiO2/ZrO2显微组织和显微硬度的影响

在Nd:YAG激光器低功率烧结的条件下,基于选择性激光烧结工艺（SLS）成形复相陶瓷Al2O3/SiO2/ZrO2材料,利用扫描电子显微镜（SEM）、X射线衍射分析仪（XRD）和显微硬度计分别对激光烧结层加入ZrO2前后的表面形貌和断口形貌、表面物相、表面显微硬度进行了分析。结果表明,部分四方相ZrO2(t-ZrO2)相变成单斜相ZrO2(m-ZrO2),应力诱导微裂纹增韧作用和Al2O3弥散强化共同作用在某种程度上提高了烧结试样的断裂韧性,对于改善零件整体寿命和可靠性有着重要的意义。     

MECHANICAL PROPERTIES AND ANTI-WEARABILITY STUDIES OF MULTILAYER THIN COATINGS ON CUTTING TOOLSS

0INTRODUCTIONhadcoatingsPlayani~troleininduStryforilnpwhngtoollifetimeandperfo~e.OneOfthe~tacandstudiedCOatingtodateisTiN,archhasboeficialPropertiesincludinghigh~ss,lowfrictionandchewhcalinertnes,[l].TiCN,incontraSttoTiN,hasbetteranti-abusiveandanti-abusivecapabilityly].BesideSfrictioncoefficients,aweax-resistantcoatingInUSthashighmicro~,hightoughneSsandadheresatisfaCtorilytotheunderlyingsuhahate.ac,theuseOfanlute~atelayertoimproVetheadheSion~theedingandthesubstratehashostudiedlsj…     

MECHANICAL PROPERTIES AND ANTIWEARABILITY STUDIES OF MULTILAYER THIN COATINGS ON CUTTING TOOLS

The nanoindentation fracture of multilayer hard coatings, such as TiN, TiN/Ti(C,N)/TiC, TiN/Ti(C,N)/TiC/Ti(C,N)/TiC and TiN/Ti(C,N)/TiC/Ti(C,N)/TiC/Ti(C,N)/TiC coatings, deposited on cemented carbide using a CVD technique are studied. It is found that these coatings have high hardness. Based on the analysis of the energy release in cracking, the fracture toughness of these coatings are calculated. The observations clearly establish a step occurs in the forcedisplacement curves at the onset of coating fracture and a straigh t line segment in the loadpenetration depth squared curves to identify the interfacial failure of coatings. The hardness, fracture toughness and antiwearability of these coatings are clearly compared. The results show that with the layes increasing, the fracture toughness and antiwearability are getting larger.     

Micro-scale abrasive wear testing of duplex and non-duplex (single-layered) PVD (Ti,Al)N, TiN and Cr–N coatings

A micro-scale abrasive wear test, based on ball-cratering, has been used to evaluate the wear resistance of duplex and non-duplex (Ti,Al)N, TiN and Cr–N coatings. The term duplex is used here when plasma nitriding is followed by PVD coating. Coatings without the plasma nitriding stage are termed single-layered. Coating properties were evaluated by surface profilometry, hardness and scratch testing. All duplex coatings showed higher micro-abrasive wear resistance than their single-layered counterparts, with the duplex (Ti,Al)N coating achieving the best performance. After a certain number of ball revolutions, the coating material became worn through, exposing the substrate material. After this point, the presence of a hard nitrided case diminished the scratching action of the SiC abrasive particles. The experimental results also indicate that the choice of the PVD coating plays an important role in improving the micro-abrasive wear resistance. Apart from single-layered and duplex Cr–N coatings, all the other coating systems provided a higher micro-abrasive wear resistance than the uncoated substrate (hardened AISI H13 steel). The poor abrasive wear resistance recorded for the single-layered and duplex Cr–N coatings could be attributed to the hardness of the Cr–N being much lower than that of the SiC abrasive particles, which caused tearing of the coating with subsequent delamination. The wear pattern observed was found to change from surfaces characterised by grooves (uncoated substrate, single-layered TiN and Cr–N systems and duplex Cr–N system) to surfaces which exhibited multiply indented surfaces (single-layered and duplex (Ti,Al)N systems), indicating a transition between wear mechanisms. This transition was found to be dependent on the ratio between the hardness of the SiC abrasive particles and surface (coating) or subsurface hardness. By decreasing this ratio, the ability of the SiC abrasive particles to scratch the composite surface was reduced and the resistance to micro-scale abrasion was improved.     

Liquid impact erosion characteristics of martensitic stainless steel laser clad with Ni-based intermetallic composites and matrix composites

NiAl-Ni₃Al intermetallic composites (IC) and intermetallic matrix composites (IMC) with TiC and WC reinforcement were laser clad to increase the liquid impact erosion resistance of AISI 420 Martensitic stainless steel. Laser process parameter optimisation and pre- and post-heat treatment of the laser clad specimens were carried out to minimise porosity and sensitivity to crack formation. The coatings were characterised by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS). The erosion resistance of the substrate material at a water droplet exit velocity of up to 150 m/s was improved from 116.9 to 838.7 min/mm³ for the nickel aluminide IC coating and from 855 to 1446 min/mm³ for the IMC coating with TiC and WC reinforcement. The pseudo-elasticity combined with the high work hardening ability was attributed to the excellent erosion resistance of nickel aluminide IC coatings. The IMC coatings with ceramic reinforcement extended significantly the initial resistance against liquid impact erosion. However, once damage occurred the erosion accelerated rapidly. No direct correlation could be established between the erosion resistance and the mechanical properties. The influence of hardness, elastic modulus, strain-hardening coefficient and the reversible penetration ratio on the erosion resistance was discussed.     

Tribotechnical and mechanical properties of Ti-Al-N nanocomposite coatings deposited by the ion-plasma method

The possibility of formation of nanocrystalline Ti-Al-N coatings using the method of ion-plasma deposition is demonstrated. The mechanical and tribotechnical characteristics of the coatings in comparison with TiN coating are studied. Ti-Al-N nanocomposite coatings possess high hardness (35 GPa) and higher wear resistance and lower wear capacity as compared to TiN coating. For a grain size of 12–15 nm the nanostructural Ti-Al-N coating has the following elemental composition: Ti ≈ 60 at %, N ≈ 30 at %, Al ≈ 10 at %. The phase composition of the coating represents the solid solution (Ti, Al)N. For this elemental and phase composition and nanograin size maximal hardness and elasticity modulus of the coating are found.     

Comparative study on tribology and microhardness of laser synthesized Ti-Al2O3/Zn coatings on Ti-6Al-4V alloy

ABSTRACT

The study of laser cladding of 90Ti-10Al₂O₃, 90Ti-8Al₂O₃-2Zn and 90Ti-4Al₂O₃-6Zn coatings onto Ti-6Al-4V alloy, with intention to produce defect-less, high microhardness and wear resistant coating was carried out. The coatings were deposited onto Ti-6Al-4V alloy at 900 W laser power and 0.6 m/min laser scan speed. Microstructures and phase constituents of the developed coatings were investigated by using a scanning electron microscope (SEM) and X-ray diffractometer correspondingly. Vickers microhardness tester and pin-on-disk tribometer were employed to characterize microhardness and wear behaviour of the Ti-Al₂O₃/Zn coatings respectively. SEM was also used to examine the worn track. It was observed that 90Ti-10Al₂O₃ coating yielded optimal microhardness along with maximal wear resistance in comparison to the other coatings and Ti-6Al-4V alloy. It has been established that laser cladding of Ti-Al₂O₃ coating with Zn contents on Ti-6Al-4V alloy alleviates the formation of cracks, however, microhardness and wear properties are negatively affected.     

Characterization of multilayer pvd nanocoatings deposited on tungsten carbide cutting tools

The present trends in the coating technologies are gradient coatings, metastable coatings, multicomponaent coatings and multilayer or super lattice coatings. The physical vapour deposition (PVD) process is well-suited technology for these advanced coating technologies. The performance of the coated tools can be improved considerably using multi-layer micro and nanocoatings. The present paper discusses the deposition and characterization of multilayer TiN/Al₂O₃ coatings on cemented tungsten carbide cutting tools using reactive sputtering. The characterization of the coatings was carried out using X-ray diffraction (XRD) for phase analysis, chemical composition using EDAX, adhesion and toughness evaluation using Rockwell indentation test and surface roughness. It was observed that with decrease in thickness of each alumina layer to nanolevel in multilayer coating system results considerable improvement in final surface finish, adhesion and toughness of the coating. The experimental results are presented and analyzed in this paper.     

Improvement of the Oxidation and Wear Resistance of Pure Ti by Laser-Cladding Ti<Subscript>3</Subscript>Al Coating at Elevated Temperature

Ti₃Al coating was in situ synthesized successfully on pure Ti substrate by laser-cladding technology using aluminum powder as the precursor. The composition and microstructure of the prepared coating were analyzed by transmission electron microscopy, scanning electron microscopy (SEM), and X-ray diffraction technique. Thermal gravimetric analysis was used to evaluate the high-temperature oxidation resistance of the Ti₃Al coating. The friction and wear behavior was tested through sliding against Si₃N₄ ball at elevated temperature of 20, 100, 300, and 500°C. The morphologies of the worn surfaces and wear debris were also analyzed by SEM and three-dimensional non-contact surface mapping. The results show that the Ti₃Al coating with high microhardness, high-temperature oxidation resistance, and high temperature wear resistance. The pure Ti substrate is dominated by severe adhesion wear, abrasive wear, fracture, and severe plastic deformation at lower temperature, and severe adhesion wear, abrasive wear, plastic deformation, oxidation, and nitriding wear at higher temperature, whereas the Ti₃Al coating experiences only moderate abrasive and adhesive wear when sliding against the Si₃N₄ ceramic ball counterpart. In addition, the wear debris of the laser-cladding Ti₃Al coating sliding and Si₃N₄ friction pairs are much smaller than that of pure Ti substrate and Si₃N₄ friction pairs at elevated temperature.     

Residual stresses in TiN, DLC and MoS2 coated surfaces with regard to their tribological fracture behaviour

Thin hard coatings on components and tools are used increasingly due to the rapid development in deposition techniques, tribological performance and application skills. The residual stresses in a coated surface are crucial for its tribological performance. Compressive residual stresses in PVD deposited TiN and DLC coatings were measured to be in the range of 0.03-4 GPa on steel substrate and 0.1-1.3 GPa on silicon. MoS₂ coatings had tensional stresses in the range of 0.8-1.3 on steel and 0.16 GPa compressive stresses on silicon. The fracture pattern of coatings deposited on steel substrate were analysed both in bend testing and scratch testing. A micro-scale finite element method (FEM) modelling and stress simulation of a 2 μm TiN-coated steel surface was carried out and showed a reduction of the generated tensile buckling stresses in front of the sliding tip when compressive residual stresses of 1 GPa were included in the model. However, this reduction is not similarly observed in the scratch groove behind the tip, possibly due to sliding contact-induced stress relaxation. Scratch and bending tests allowed calculation of the fracture toughness of the three coated surfaces, based on both empirical crack pattern observations and FEM stress calculation, which resulted in highest values for TiN coating followed by MoS₂ and DLC coatings, being K_C = 4-11, about 2, and 1-2 MPa m^1/2, respectively. Higher compressive residual stresses in the coating and higher elastic modulus of the coating correlated to increased fracture toughness of the coated surface.     

真空阴极电弧沉积（Ti,Al）N薄膜的应用研究

为了提高TiN涂层刀具的耐磨性,采用钛铝合金靶,以真空阴极电弧沉积法制备了（Ti,Al)N涂层,对膜层形貌成分,组织结构及硬度进行了测试及研究,并试验了（Ti,Al)N涂层高速钢钻头及YG6硬质合金刀具的使用寿命,结果表明：（Ti,Al)N涂层硬度高达HV0．1,15,3700,（Ti,Al)N涂层使高速钢钻头及YG6硬质合金刀具的使用寿命显著提高。     

Influence of WC size and HVOF process on erosion wear performance of WC-10Co4Cr coatings

In the present study, based on the velocity and temperature measurements of in-flight particles and parameter optimization, multimodal and conventional WC-10Co4Cr cermet coatings were sprayed by high velocity oxygen gas fuel spraying (HVOGF) and high velocity oxygen liquid fuel spraying (HVOLF). The coatings’ structure, porosity, microhardness and fracture toughness were investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) etc. Furthermore, erosion resistance of the coatings to solid sand was tested, followed by the exploration of the material failure mechanisms. Results show that the WC-10Co4Cr coatings deposited by HVOLF are mainly composed of WC with no obvious decarburization and amorphous CoCr binder. The mechanical properties of the coatings deposited by HVOLF are much more superior to those deposited by HVOGF. Multimodal WC-10Co4Cr coating deposited by HVOLF possesses the highest microhardness and fracture toughness, the lowest porosity and the most excellent resistance to sand solid erosion wear, which was enhanced by 15 and 40% than that of HVOLF conventional coatings at 30° and 90° impact angles. The improvement is even greater in comparison with multimodal coating deposited by HVOGF. These results have provided important reference for WC-CoCr anti-erosion coating design and optimization of high velocity oxygen fuel (HVOF) process.     

Y2O3改性石墨/CaF2/TiC/镍基合金复合涂层微观组织与摩擦学性能研究

为提高石墨/CaF₂/TiC/镍基合金（GCTN）复合涂层的力学性能和摩擦学性能,运用等离子喷涂技术在45钢表面制备了Y₂O₃改性GCTN复合涂层,研究了Y₂O₃对复合涂层的微观组织、显微硬度、断裂韧性和摩擦磨损性能的影响。结果表明：Y₂O₃改性GCTN复合涂层主要由γ-Ni、CrB、Cr7C₃、TiC、CaF₂和石墨等物相组成。Y₂O₃在等离子火焰加热作用下与C元素反应生成活性元素Y,Y净化了复合涂层的微观组织,并细化了CrB、Cr₃C7等硬质相晶粒,提高了其致密性。当Y₂O₃质量分数为0.5%时,复合涂层的显微硬度和断裂韧性分别为593.3MPa和6.82MPa·m^1/2,比不含Y₂O₃的复合涂层分别增大了8%和22%,其机理主要是Y₂O₃细化了CrB、Cr₃C₇等硬质相晶粒,起到了细化强化作用。由于GCTN-0.5Y₂O₃复合涂层的显微硬度和断裂韧性显著提高,减少了其黏着磨损和微观断裂磨损,因而GCTN-0.5Y₂O₃复合涂层的摩擦因数和磨损率最小,分别为0.085和0.39×10-3mm3/m。     

热喷涂纳米结构Al2O3／TiO2涂层断裂韧性的统计性质

采用压痕裂纹法测定了等离子喷涂纳米结构Al2O3／TiO2涂层的断裂韧性及其统计离散度。研究表明,采用不同载荷获得的压痕韧性呈现出较大的离散性,其分布符合韦伯分布类型。通过分析指出,随着载荷的增大压痕韧性的数值趋于集中,而导致压痕韧性产生较大波动性的根本原因在于涂层之中显微结构的不均匀性。     

TiN/TiSiN复合涂层显微结构与力学性能研究

采用工业用直流脉冲等离子体增强化学气相沉积(PCVD)法在硬质合金刀具基体上制备了TiN和TiN/TiSiN复合涂层.对TiN涂层和不同沉积温度下制备的三种TiN/TiSiN复合涂层的微观结构和力学性能进行了对比研究.结果表明:随着沉积温度的升高,TiN/TiSiN复合涂层的结合力增大;沉积温度为550℃时,TiN/T...     

C离子注入对硬质合金刀具TiN涂层性能的影响

在硬质合金刀具上沉积了PVD—TiN涂层,并采用C离子注入技术对其进行表面改性处理。对涂层截面的微观形貌、显微硬度以及与基体附着力的测试结果表明,C离子注入可使TiN涂层的显微组织细密均匀化,并能明显提高涂层的显微硬度以及与基体的附着力。     

Wear characteristic of in situ synthetic TiB2 particulate-reinforced Al matrix composite formed by laser cladding

In order to improve the wear resistance of an aluminum alloy, an in situ synthesized TiB₂ particulate-reinforced metal matrix composite coating was formed on a 2024 aluminum alloy by laser cladding with a powder mixture of Fe-coated boron, Ti and Al was successfully achieved using a 3-kW CW CO₂ laser. The chemical composition, microstructure and phase structure of the composite clad coating were analyzed by energy dispersive X-ray spectroscopy (EDX), SEM, TEM and XRD. The nanohardness and the elastic modulus of the phases of the coating have been examined. The dry sliding wear behaviour of the coating was investigated using a pin-on-ring machine under four loads, namely 8.9, 17.8, 26.7, and 35.6 N. It has been found that the wear characteristics of cladding were completely dependent on the content and morphology of the TiB₂ particulate and intermetallic in the microstructure and the applied load. At the lowest load (8.9 N), with increasing content of TiB₂ particulate and intermetallic, the wear weight loss of the laser cladding was decreased. At higher loads (17.8, 26.7, and 35.5 N), the 2024 Al alloy exhibited superior wear resistance to the particle-reinforced metal matrix composite cladding.     

Development of nano-structured Al2O3-TiB2-TiN coatings by combined SHS and laser surface alloying

A powder mixture of aluminium (Al), titania (TiO₂) and hexa-boron nitride (h-BN) was laser-triggered to undergo SHS (self-propagating high temperature synthesis) and was subsequently laser alloyed onto a mild steel substrate surface. A nano-structured coating was formed with high microhardness (～3000 HV_0.05 at the cross-section and ～2600 HV_0.2 on the top surface). X-ray diffraction (XRD) identified the presence of aluminium oxide (Al₂O₃), titanium di-boride (TiB₂), titanium nitride (TiN), iron (Fe) and its borides (FeB, Fe₂B) in the coating. Scanning electron microscopy (SEM) and high resolution transmission electron microscopic (HRTEM) analysis of the coating revealed nano-fibrous titanium-rich reinforcements in a matrix of nano-crystalline alumina. The thickness of titanium di-boride nano-fibres was an order of magnitude higher than the size of nano-alumina crystallites.     

Two-body abrasive wear of electroless nickel composite coatings

The two-body abrasive wear of electroless nickel (EN), EN-silicon carbide, and EN-alumina composite coatings have been investigated using a scratch test with a diamond indenter. The coatings were heat treated at temperatures of 100–500° C. The hardness of the coatings increased with heat treatment temperature from 500 HV100 for the as-deposited condition to 1008 HV100 when fully hardened. Scratch testing showed that the as-deposited coating had scratch tracks with a high degree of plasticity, signs of microploughing and tensile cracking and was characterised as a ductile failure. On the other hand, the heat-treated coatings showed chipping and cracking on the edge of the scratch tracks, failing in a brittle manner. The heat-treated EN-silicon carbide coatings, however, exhibited no cracking nor chipping, believed to be due to its higher fracture toughness than the other heat-treated coatings, attributable to its lower phosphorus content. The volume of material removed from the silicon carbide scratch track was 1/3 of the volume removed from the steel substrate at a 20 N load, and showed the best wear/ scratch resistance of any of the coatings tested.     

Finite element modelling of brittle fracture of thick coatings under normal and tangential loading

This paper addresses coating fracture in hard brittle coatings subjected to combined normal and tangential loads through a finite element based methodology. The coating is modelled as an elastic layer perfectly bonded to an elastic substrate with a pre-microcrack, assumed to initiate at the contact trailing edge due to high tensile stress. The predicted results are consistent with previously published coating fracture results. The model predicts a significant effect of coating thickness on crack propagation for coatings with large elastic mismatch and the final propagated crack profile is predicted to depend on friction coefficient, coating fracture toughness and sliding displacement.