Effect of Annealing Temperature on Tribological Properties and Material Transfer Phenomena of CrN and CrAlN Coatings

This study evaluates the effects of annealing temperature and of the oxides produced during annealing processes on the tribological properties and material transfer behavior between the PVD CrN and CrAlN coatings and various counterface materials, i.e., ceramic alumina, steel, and aluminum. CrAlN coating has better thermal stability than CrN coating in terms of hardness degradation and oxidation resistance. When sliding against ceramic Al₂O₃ counterface, both CrN and CrAlN coatings present excellent wear resistance, even after annealing at 800 °C. The Cr-O compounds on the coating surface could serve as a lubricious layer and decrease the coefficient of friction of annealed coatings. When sliding against steel balls, severe material transfer and adhesive wear occurred on the CrN and CrAlN coatings annealed at 500 and 700 °C. However, for the CrAlN coating annealed at 800 °C, much less material sticking and only small amount of adhesive wear occurred, which is possibly due to the formation of a continuous Al-O layer on the coating outer layer. The sliding tests against aluminum balls indicate that both coatings are not suitable as the tool coatings for dry machining of aluminum alloys.     

Effect of Thermal Annealing on Tribological and Corrosion Properties of DLC Coatings

In this study, the mechanical, tribological, and corrosion properties of annealed diamond-like carbon (DLC) coatings on M2 steel with various annealing temperatures were investigated. The results indicated that DLC coating on M2 steel annealed at 500 °C had the worst performance. Both corrosion polarization resistance and wear resistance against ceramic alumina counterface of DLC coatings decreased with increasing annealing temperature, which can be due to the decline of the coating hardness after the thermal treatment. When sliding against aluminum counterface material, the DLC annealed at 600 °C had the lowest coefficient of friction (cof) and wear resistance due to its high graphitic structure and low hardness. Compared with the original coating, cofs increased for coatings treated at below 300 °C; however, further increasing the annealing temperature led to the decrease of the cofs. Little material attachment occurred between DLC coatings (original and annealed) and counterface materials (both alumina and aluminum balls) except for the DLC annealed at 600 °C, in which coating material transferred to the surface of counterface ball.     

The effect of annealing on microstructure and tensile properties of Ti–22Al–25Nb electron beam weld joint

This study investigated the microstructure evolution and tensile properties of Ti–22Al–25Nb EBW joints. The fusion zone of the as-welded joint exhibited a fully B₂ microstructure. Widmanstätten O particles precipitated out of B₂ matrix after annealing and their size increased within a temperature range from 750 °C to 900 °C. In the heat affected zone, there was a transition of microstructure moving away from the fusion zone towards the base material. Strength and elongation of the as-welded sample were significantly improved after annealing, which was attributed to the strengthening effect of O precipitates and the slip transmission between O and B₂ phases. Samples tensile tested at 650 °C all failed within the fusion zone and exhibited intergranular failure instead of transgranular failure at room temperature. The room temperature strength and hardness of the joints decreased with annealing temperature due to the coarsening of O precipitates. At 650 °C, failure occurred by intergranular fracture in the fusion zone and the joint strength of all annealed samples was similar due to similar B₂ grain boundary strength.     

Annealing Effect on the Intermetallic Compound Formation of Cold Sprayed Fe/Al Composite Coating

A Fe/Al composite coating was prepared by cold spraying using an iron-aluminium powder mixture with a Fe/Al atomic ratio of 1:1. The effect of annealing temperature on the intermetallic compound formation in the cold-sprayed Fe/Al coating was investigated. The as-sprayed and annealed coatings were characterized by x-ray diffraction (XRD), and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy. Results showed that intensive particle deformation on impact promoted the Fe₂Al₅ intermetallic compound formation at a low annealing temperature of 450?°C and this intermetallic layer firstly appeared along some intimate contact regions at the aluminium-iron boundaries. The amount of the Fe₂Al₅ intermetallic compound increased and no other intermetallic compound phases appeared when the annealing temperature was raised from 450 to 600?°C. Some cracks developed in the Fe₂Al₅ intermetallic layer when the coating was annealed at 600?°C and the possible causes leading to evolution of cracks are discussed.     

Electrochemical evaluation of the corrosion protectiveness and porosity of vacuum annealed CrAlN and TiAlN cathodic arc physical vapor deposited coatings

The corrosion behavior of cathodic arc physical vapor deposited CrAlN and TiAlN coatings were examined in 1 M HCl solution before and after vacuum annealing at 700, 800, 900, and 1000 °C. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) methods were used to study the corrosion behavior and porosity of the coatings in comparison with the bare steel substrate (304SS). Structural and mechanical characterization of the coatings were also conducted. It is found that with increasing annealing temperature, the mechanical properties of TiAlN increased due to age hardening caused by spinodal decomposition while the hardness of CrAlN decreased as result of relaxation. Similarly, EIS and PDP results revealed that the as‐deposited and annealed coatings offer higher corrosion resistance as compared to the bare 304SS substrate. The coatings susceptibility to corrosion is reduced after annealing as indicated by the increasing nobility of E_corr. Both PDP and EIS tests revealed that CrAlN coating annealed at 1000°C exhibited superior corrosion resistance properties. It is found that the reduced current density for CrAlN coating annealed at 1000°C was due to the reduction in the porosity. Annealed TiAlN coating follows similar behavior until an optimum annealing temperature of 800°C. Beyond this temperature, porosity enlargement and an increase in the number of pores subsequent to structural changes deteriorated the corrosion resistance of TiAlN coating.     

Effect of immersion Ni plating on interface microstructure and mechanical properties of Al/Cu bimetal

A nickel-based coating was deposited on the pure Al substrate by immersion plating, and the Al/Cu bimetals were prepared by diffusion bonding in the temperature range of 450–550 °C. The interface microstructure and fracture surface of Al/Cu joints were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The mechanical properties of the Al/Cu bimetals were measured by tensile shear and microhardness tests. The results show that the Ni interlayer can effectively eliminate the formation of Al-Cu intermetallic compounds. The Al/Ni interface consists of the Al₃Ni and Al₃Ni₂ phases, while it is Ni-Cu solid solution at the Ni/Cu interface. The tensile shear strength of the joints is improved by the addition of Ni interlayer. The joint with Ni interlayer annealed at 500 °C exhibits a maximum value of tensile shear strength of 34.7 MPa.     

Tensile strength of plasma-sprayed alumina and/or zirconia coatings on titanium

The heat treatment effect on the characteristics and tensile strength of plasma-sprayed alumina, yttria-stabilized zirconia (YSZ), and mixtures of alumina and YSZ coatings on titanium was investigated. The as-sprayed structures of alumina and YSZ coatings consists of a and y alumina phases, and cubic and tetragonal zirconia phases, respectively. The tensile strength of the coatings containing a large amount of YSZ is increased from 25 to 50 MPa by heat treatment at 800 °C. The 60% YSZ-AI₂O₃ coating showed the highest tensile strength. The tensile strength increase of the YSZ-containing coating by heat treatment is caused by formation of 10 to 100 nm wide microcracks. The interface adhesion strength between the heat-treated titanium substrate and the alumina-containing coating is increased by chemical reaction at the in-terface. Thus, a heat-treated alumina and zirconia mixture coating may be favorable in obtaining high tensile strength due to microcrack formation in the coating and the chemical reaction at the interface. During this work, S. Baba was a graduate student at Kyushu Institute of Technology, Sumitomo Metal Ind. Ltd., Osaka, Japan.     

Elevated Temperature Solid Particle Erosion Performance of Plasma-Sprayed Co-based Composite Coatings with Additions of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and CeO<Subscript>2</Subscript>

In this paper, investigation into solid particle erosion behavior of atmospheric plasma-sprayed composite coating of CoCrAlY reinforced with Al₂O₃ and CeO₂ oxides on Superni 76 at elevated temperature of 600 °C is presented. Alumina particles are used as erodent at two impact angles of 30° and 90°. The microstructure, porosity, hardness, toughness and adhesion properties of the as-sprayed coatings are studied. The effects of temperature and phase transformation in the coatings during erosion process are analyzed using XRD and EDS techniques. Optical profilometer is used for accurate elucidation of erosion volume loss. CoCrAlY/CeO₂ coating showed better erosion resistance with a volume loss of about 50% of what was observed in case of CoCrAlY/Al₂O₃/YSZ coating. Lower erosion loss is observed at 90° as compared to 30° impact angle. The erosion mechanism evaluated using SEM micrograph revealed that the coatings experienced ductile fracture exhibiting severe deformation with unusual oxide cracks. Reinforced metal oxides provide shielding effect for erodent impact, enabling better erosion resistance. The oxidation of the coating due to high-temperature exposure reforms erosion process into oxidation-modified erosion process.     

Effect of Annealing Temperature on Microstructure and Mechanical Properties of Hot Swaged cp-Ti Produced by Investment Casting

The purpose of this study is to evaluate the influence of hot swaging (SW) and annealing treatment on microstructure and mechanical properties of commercially pure titanium (grade 4) produced by investment casting. During SW at 700 °C, the diameter of the cast titanium bars was reduced from 25 to 8.5 mm in 14 steps. After SW, material was annealed for 1 h at 500, 700, or 870 °C. The as-cast samples showed a typical microstructure consisting of a variety of α-morphologies, while the hot swaged samples exhibited a kinked lamellar microstructure. Annealing at 500 °C did not significantly change this microstructure, while annealing at both 700 and 870 °C led to recrystallization and formation of equiaxed microstructures. The cast bars exhibited a typical hard α-layer in near-surface regions with maximum depth and maximum hardness of 720 μm and 660 HV0.5, respectively. Due to SW, the tensile strength of the as-cast material drastically increased from 605 to 895 MPa. Annealing at 500 °C decreased this tensile strength slightly from 895 to 865 MPa while annealing at 700 °C led to a further pronounced drop in tensile strength from 865 to 710 MPa. No additional decrease in tensile strength was observed by increasing the annealing temperature from 700 to 870 °C. The tensile ductility of the as-cast and hot swaged samples was approximately the same in the range of 0.05 to 0.11, while the annealed samples showed values in the range of 0.25 to 0.53. In addition, the as-cast and hot swaged samples revealed a brittle cleavage fracture surfaces. However, the annealed samples showed a transgranular ductile fracture with formation of dimples.     

The Influence of Temperature on Frictional Behavior of Plasma-Sprayed NiAl-Cr2O3 Based Self-Adaptive Nanocomposite Coatings

Frictional behavior of nano and hybrid-structured NiAl-Cr₂O₃-Ag-CNT-WS₂ adaptive self-lubricant coatings was evaluated at a range of temperatures, from room temperature to 700 °C. For this purpose, hybrid structured (HS) and nanostructured (NS) composite powders with the same nominal compositions were prepared by spray drying and heat treatment techniques. A series of HS and NS coating samples were deposited on steel substrate by an atmospheric plasma spraying process. The tribological behavior of both coatings was studied from room temperature to 700 °C at 100° intervals using a custom designed high temperature wear test machine. Scanning electron microscopy was employed for the evaluation of the composite coatings and worn surfaces. Experimental results indicated that the hybrid coating had inferior tribological properties when compared to the nanostructured coating, showing the attractive frictional behavior on the basis of low friction and high wear resistance; the NS coating possessed a more stable friction coefficient in the temperature range of 25-700 °C against alumina counterface. Microstructural examinations revealed more uniformity in NS plasma-sprayed coatings.     

Thermal Stability of Microstructure and Hardness of Cold-Sprayed cBN/NiCrAl Nanocomposite Coating

cBN/NiCrAl nanocomposite coatings were deposited by cold spraying using mechanically alloyed composite powders. To examine their thermal stability, the nanocomposite coatings were annealed at different temperatures up to 1000?°C. The microstructure of composite coatings was characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results showed that the nanostructure can be retained when the annealing temperature is not higher than 825?°C, which is 0.7 times of the melting point of the NiCrAl matrix. The dislocation density was significantly reduced when the annealing temperature was higher than 750?°C. The reaction between cBN particles and the NiCrAl matrix became noticeable when the annealing temperature was higher than 825?°C. The effects of grain refinement and work-hardening strengthening mechanisms were quantitatively estimated as a function of annealing temperature. The influence of annealing temperature on the contribution of different strengthening mechanisms to coating hardness was discussed.     

Effect of substrate temperature and nitrogen concentration during sputtering on corrosion behaviour of AlN coatings

Aluminium nitride coatings were formed on stainless steel substrate by DC-reactive balanced magnetron sputtering at various nitrogen concentrations in the sputtering gas mixture, and different substrate temperatures. The electrochemical corrosion behaviour of the coatings obtained was studied in 0.5?M H₂SO₄. Continuous improvement in corrosion resistance of the coatings was observed with increasing coating deposition temperature up to 500?°C. The corrosion potential shifted from ?0.66 V_SCE at 100?°C to ?0.33?V_SCE at 500?°C. Accordingly, the corrosion current density decreased significantly with increase in the deposition temperature. However, no major difference in corrosion behaviour could be noticed for the coatings formed at various nitrogen concentrations.     

精密铸造工业纯Ti的力学性能

研究了热旋锻和退火处理对精密铸造工业纯钛显微组织和力学性能的影响。铸造样品为典型的含有不同形貌的α相组织;而旋锻样品是缠绞的层状组织。在500°C退火处理不会显著改变样品的显微组织,但在700°C和870°C退火会导致再结晶发生和生成等轴晶组织。铸造棒在近表层生成典型的硬化α层,其最大深度达720μm,最大硬度达HV0.5660。旋锻能使铸造样品的拉伸强度从605MPa增加到895MPa。在500°C退火会导致拉伸强度轻微降低,从895MPa降到865MPa。然而在700°C退火会导致拉伸强度显著下降,从865MPa降到710MPa。当退火温度升高到870°C时,拉伸强度的下降不再明显。铸造和热旋锻样品的断裂应变在0.05~0.12的范围内,而退火后的样品在0.25~0.53的范围。铸态和旋锻态样品表现为脆性解理断裂,而退火态样品为穿晶塑性断裂,伴有韧窝的生成。     

Morphology,Structure, Microhardness and Corrosion Resistance of Ni-W Coating Annealed in Hydrogen and Argon Atmosphere

In this paper, an amorphous Ni-W coating was electrodeposited on the low-carbon steel and then annealed in hydrogen and argon atmosphere. Their characterization was carried out using scanning electron microscopy and x-ray diffraction. The corrosion characterization was carried out using the potentiodynamic polarization (Tafel) and electrochemical impedance spectroscopy. The results show that microcracks inevitably exist on the surface of Ni-W coating when annealed at 750 °C or higher temperature. After annealing treatment, amorphous structure transforms to crystalline and some new phases are precipitated, which is significantly affected by the annealing temperature and atmosphere. The microhardness of annealed Ni-W coatings is much higher than that of as-deposited coating, while an adverse corrosion performance is observed for the annealed Ni-W coatings. The coating annealed in hydrogen at 500 °C shows a huge improvement in hardness and a fairly acceptable corrosion resistance compared with the as-deposited Ni-W coating.     

Mechanical and Microstructural Characterization of Cold-Sprayed Ti-6Al-4V After Heat Treatment

The cold spray of Ti-6Al-4V coatings deposited on Ti-6Al-4V substrates has been investigated. Coatings were produced using nitrogen and helium as propellant gases and subsequently heat treated with various temperature-time conditions. The microstructure was characterized by SEM and optical microscopy while mechanical properties were measured by microhardness and tensile testing. It is shown that coatings sprayed with nitrogen gas were relatively porous in comparison to the nearly completely dense coatings obtained with helium gas. In the as-sprayed condition, coatings displayed high hardness but low tensile strength. Heat treatments at temperatures of 600 °C and higher resulted in a decrease in hardness due to microstructural changes within the particles including recovery, recrystallization, and/or phase transformation. However, an increase in tensile strength was attributed to improved inter-particle bonding due to an observed change from brittle to ductile features on the fracture surface. The highest strength coating produced was a helium-sprayed coating annealed at 600 °C, which featured a tensile strength ~85% of the minimum required bulk value and coating/substrate microstructures similar to the as-received powder/substrate microstructures.     

B4 C 含量对等离子喷涂 NiCoCrAlY / Al2 O3 -B4 C复合涂层力学性能的影响

目的提高等离子喷涂NiCoCrAlY/Al2O3复合涂层的摩擦性能。方法采用离心喷雾造粒、化学冶金包覆和固相合金化技术制备NiCoCrAlY/Al2O3和NiCoCrAlY/B4C复合粉体,通过等离子喷涂技术制备NiCoCrAlY/Al2O3-B4C复合涂层。对涂层的显微结构、结合强度和显微硬度进行表征,研究B4C含量对等离子喷涂NiCoCrAlY/Al2O3-B4C复合涂层力学性能的影响。结果 Al2O3和B4C颗粒包覆了致密的NiCoCrAlY合金层,包覆层厚约3~5μm。等离子喷涂NiCoCrAlY/Al2O3-B4C复合涂层呈典型的层状结构,涂层结构致密,各层间结合良好。随着B4C含量的增加,复合涂层的显微硬度逐渐增大,结合强度逐渐降低,当B4C质量分数达到30%时,涂层的显微硬度比未添加B4C时提高了1.4倍,结合强度比未添加B4C时降低了26%。涂层在拉伸试验中发生了典型的脆性断裂,断裂位置发生在涂层内部。结论向等离子喷涂NiCoCrAlY/Al2O3复合涂层中添加B4C,可显著提高涂层的显微硬度,但会使涂层的结合强度有一定程度降低。     

钼添加对CrN涂层抗氧化性能的影响

研究钼添加对CrN涂层微观结构和抗氧化性能的影响,采用反应磁控溅射法在硅片和高速钢片上制备不同Mo含量的Cr-Mo-N涂层,并在500~800 ℃的高温空气中退火1 h,用X射线衍射（XRD）、拉曼光谱和扫描电子显微镜（SEM）对涂层退火前后的微观形貌进行表征。沉积的CrN和Cr-Mo-N涂层均表现出基于CrN晶格的B1面心立方相（fcc）。Mo离子取代Cr-N晶格中的Cr离子,形成Cr-Mo-N固溶体。在600 ℃时,XRD和拉曼光谱表明,Mo含量较高的Cr-Mo-N涂层中形成MoO₃相,表面较粗糙,含氧量较高。在700 ℃时,CrN涂层由于内应力的作用,其横截面形貌为疏松的柱状晶,并有一定的多孔区,而Cr-Mo-N涂层则为致密的柱状晶结构。低Mo含量（<17at%）的Cr-Mo-N涂层比CrN涂层具有更好的抗氧化性。     

Influence of deposition temperature on mechanical properties of plasma-sprayed hydroxyapatite coating on titanium alloy with ZrO<Subscript>2</Subscript> intermediate layer

Hydroxyapatite coatings were plasma sprayed on the Ti6A14V substrate with and without an intermediate ZrO₂ layer; meanwhile the temperatures of substrates were varied at 90, 140, and 200 °C. The coatings were subjected to the standard adhesion test per ASTM C633-79. The purpose of the investigation was to study the effects of those processing variables on the bonding strength and failure behavior of the system. It is found that the bonding strengths of HA/ZrO₂ and HA coatings generally decrease with increasing substrate temperature, except for the HA/ZrO₂ coating deposited at 200 °C. The rationale of the results is attributed to the residual stress reported in the literature. Introducing ZrO₂ bond coat is found to significantly promote the bonding strength of HA coating. The possible strengthening mechanism is the rougher surface of ZrO₂ bond coat and the higher toughness of ZrO₂, which provide the mechanical strengthening effects. The slightly denser HA in 200 °C deposited HA coating cannot explain the high bonding strength of the HA/ZrO₂ coating, nor the mechanical strengthening effect of ZrO₂ intermediate layer should apply. It is believed that a stronger diffusion bonding is formed at the interface of HA and ZrO₂, which increases the bonding between them chemically. The bonding strengths of HA/ZrO₂ and HA coatings are correlated with the area fraction of adhesive failure of the coatings. The correlation explains the findings in this study.     

Influence of Post-Weld Annealing on Transformation Behavior and Mechanical Properties of Laser-Welded NiTi Alloy Wires

The influence of annealing on the transformation behavior, mechanical, and functional properties of laser-welded NiTi wires was investigated. The results show that Ti₃Ni₄ precipitates occur after post-weld annealing and coarsen with increasing annealing temperature. The as-welded specimen exhibits one-step B2 → B19′ transformation, while the annealed ones show two-step B2 → R → B19′ transformation. Annealing at 400 °C for 1 h can improve the tensile strength and superelasticity of the welded joints. However, these properties decrease when annealing at 500 °C for 1 h. The change of mechanical and functional properties after annealing is attributed to the different size of Ti₃Ni₄ precipitates. Annealing to produce smaller coherent precipitates (10 nm) improves the mechanical and functional properties of the welded joints. As the Ti₃Ni₄ precipitates coarsen, the mechanical and functional properties decrease.     

Comparison of corrosion resistance between Al2O3 and YSZ coatings against high temperature LiCl-Li2O molten salt

In this study, the high-temperature corrosion resistance of plasma-sprayed ceramic oxide coatings has been evaluated in a LiCl-Li₂O molten salt under an oxidizing environment. Al₂O₃ and YSZ coatings were manufactured by atmospheric plasma spraying onto a Ni alloy substrate. Both the plasma-sprayed Al₂O₃ and YSZ coatings had a typical splat quenched microstructure which contained various types of defects, including incompletely filled pores, inter-splat pores and intra-splat microcracks. Corrosion resistance was evaluated by the thickness reduction of the coating as a function of the immersion time in the LiCl-Li₂O molten salt at a temperature of 650 °C. A linear corrosion kinetic was found for the Al₂O₃ coating, while no thickness variation with time occurred for the YSZ coating. The ceramic oxide coatings were reacted with LiCl-Li₂O molten salt to form a porous reaction layer of LiAl, Li₅AlO₄ and LiAl₅O₈ for the Al₂O₃ coating and a dense reaction layer of non-crystalline phase for the YSZ coating. The reaction products were also formed along the inside coating of the porous channel. The superior corrosion resistance of the YSZ coating was attributed to the formation of a dense protective oxide layer of non-crystalline reaction products on the surface and at the inter-splat pores of the coating.