Structure and hardness of titanium surfaces carburized by pulsed laser melting with graphite addition

Titanium foils coated with graphite films 20 μm thick were irradiated by means of a pulsed Nd-YAG in order to harden this metal by surface melting and alloying. The relationships between irradiation parameters, microstructure and hardness of the synthesized composite coatings were determined. Four relevant parameters were defined as governing the irradiation processes. The parametric working field of the laser source was investigated next to its periphery. The influences of the relevant irradiation parameters on the microstructure and hardness of the melted zone were deduced from the metallographic analyses and Vickers micro-indentation tests of the cross sections of this composite zone. Such a zone was constituted always with hard titanium carbide and ductile metallic titanium, some times with the presence of lubricating graphite inclusions. The main advantage of such a surface treatment of titanium is to synthesize, under clearly defined irradiation conditions, a self-lubricating composite coating that resists abrasive or adhesive wear.     

Microstructure and wear properties of AISI 1020 steel surface modified by HARDOX 450 and FeB powder mixture

The effects of gas tungsten arc-processing (GTA) was used for developing wear resistance of AISI 1020 steel substrate. Appropriate quantities of FeB powder and Hardox 450 were combined to create conditions that synthesize particles into reinforced Fe-based composite surface coating. The phase transformations on new created coated surfaces were comprehensively examined by using a combination of scanning electron microscopy (SEM), microanalysis by energy dispersive spectrometry (EDS), X-Ray diffraction (XRD), microhardness and abrasive wear tests. The microstructure studies of the superficial layers of the coating revealed presence of a mixture of the dendritic phase structure of ferrit (α) and FeB-Fe₂B-Fe₃B borides. The results show that; the size of dendrites formed in the coated surface, the change of hardness of the coated surfaces, the borides volume rate and thickness of the coating changed by the variation of the processing parameters. The studies concluded that Hardox 450 + 40 wt % FeB composite coating was the most appropriate combination in terms of hardness and wear performance.     

Influence of niobium and molybdenum addition on microstructure and wear behavior of laser-borided layers produced on Nimonic 80A-alloy

Laser alloying was used for production of thick layers on surface of Nimonic 80A-alloy. For laser surface modification, three types of pre-coated pastes were applied: with amorphous boron, with amorphous boron and molybdenum as well as with amorphous boron and niobium. The microstructure, hardness and wear resistance of produced layers were studied in details. The presence of different types of borides in re-melted zone depended on the paste composition and caused an increase in hardness up to about HV 1000. The wear resistance was evaluated by calculation of mass wear intensity factor I_mw and relative mass loss of specimen and counter-specimen. The wear behavior of the tested frictional pairs was determined by 3D interference microscopy, scanning electron microscopy equipped with EDS microanalyzer. The significant increase in abrasive wear resistance was observed in comparison to untreated Nimonic 80A-alloy. The lowest mass loss intensity factor was characteristic of laser-alloyed Nimonic 80A-alloy with boron and niobium (I_mw=1.234 mg/(cm²·h)). Laser alloyed-layers indicated abrasive wear mechanism with clearly visible grooves. Laser alloying with boron and niobium resulted in the additional oxidative wear mechanism. In this case, EDS patterns revealed presence of oxygen on the worn surface of specimen.     

Surface modification of atmospheric plasma sprayed cermet coatings by plasma transferred arc method

ABSTRACT

AISI 8620 steel substrates were coated with WC–Co and Cr₃C₂–NiCr by using the atmospheric plasma spraying (APS) method. Subsequently, surface melting of samples coated with APS was performed at different current values using the plasma transfer arc (PTA) method. Microstructure, microhardness, and wear properties of as-sprayed and surface-modified coatings were investigated. The microstructure of the APS-coated surface had some voids, cracks and nonhomogeneous areas. These defects were eliminated with the PTA surface modification process and microstructural properties of coatings were improved. The wear resistance of PTA modified coatings was also increased. The highest wear resistance and microhardness were obtained in WC–Co coating modified by PTA at a current of 80?A. The wear resistance of this coating was 8.5 times higher than that of the substrate. The coating hardness reached values as high as 980?HV_0,1 in this coating.     

纳米稀土CeO2掺杂对Ni-Fe-Co-P合金镀层性能的影响

利用喷射电沉积技术制备了Ni-Fe-Co-P-CeO_2复合镀层。通过SEM、XRD、EDS等测试了复合镀层的表面形貌、截面形貌、物相结构和组成成分,同时,表征了复合镀层的硬度、耐磨和耐蚀性能,探究和分析了纳米稀土CeO_2颗粒浓度对镀层性能的影响。结果表明:该多元复合镀层为非晶态结构;随着镀液中CeO_2颗粒浓度的增加,复合镀层的显微硬度、耐磨性和耐蚀性均呈先增强后减弱的趋势;镀液中CeO_2颗粒浓度为1 g/L时,复合镀层的表面均匀致密,其HV_(0.1)显微硬度达到最大值5982 MPa,且具有最优的耐磨和耐蚀性能。     

Structural Relaxation and Nanocrystallization-Induced Laser Surface Hardening of Fe-Based Bulk Amorphous Alloys

Amorphous metallic alloys or bulk metallic glasses are emerging as promising materials for a range of structural, microelectromechanical systems, and biomedical applications. With the recent developments in spark plasma sintering and superplastic forming of the amorphous alloys, it is likely that the amorphous alloys will find a place in new applications. In this article, surface hardening of spark plasma sintered Fe₄₈Cr₁₅Mo₁₄Y₂C₁₅B₆ bulk amorphous alloys using a continuous-wave Nd:YAG laser is reported. Depending on the processing parameters, the laser surface irradiation causes structural relaxation (enhanced medium-range ordering and/or annihilation of excess free volume) and nanocrystallization of hard carbides (M₂₃C₆ and M₇C₃), resulting in surface hardening. Detailed investigations on the thermal effects, microstructural modifications, and hardness improvements due to laser surface irradiation with laser fluence in the range of 1.77–2.36 J/mm² are presented. An increase in hardness in the range of 1360–1560 HV for laser surface-treated alloys compared to 1200 HV for as-sintered alloys over a hardening depth of about 50–80 µm is observed.     

Properties of alumina-titania coatings prepared by laser-assisted air plasma spraying

Studies have shown that microstructures formed by post-laser remelting of air plasma sprayed coatings exhibit densification but also numerous macrocracks due to the rapid cooling and thermal stresses. In laser-assisted air plasma spraying (LAAPS) process, the laser beam interacts simultaneously with the plasma torch in order to increase the temperature of the coating and possibly remelt the coating at the surface. As a result, the microstructure is partially densified and macrocracks, which are generally produced in the post-laser irradiation treatment, may be inhibited. In this paper, LAAPS was performed to improve the hardness and wear resistance of Al₂O₃-13%TiO₂ coatings. These coatings prepared by air plasma spraying (APS) are widely used to protect components against abrasive wear at low temperatures. The coating microstructure was characterized by SEM and X-ray diffraction. The mechanical characterization was done by hardness measurements, erosive wear tests and abrasion wear tests. Results showed that laser assistance may improve the microstructural and mechanical properties. Phenomena involved in LAAPS of alumina-titania coatings are discussed in this paper.     

Laser remelting of plasma-sprayed yttria partially stabilized zirconia coatings

A plasma-sprayed 8 wt.% yttria partially stabilized zirconia coating doped with 3 wt.% SiO₂ was remelted by laser. The microstructure of the as-sprayed and laser-remelted coatings was characterized by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), transmission electron microscopy (TEM), and x-ray diffraction (XRD). The effect of laser remelting on the hardness, wear resistance, and thermal shock resistance of the coatings was also studied. The laser-remelted coating consists of fine solidification grains without the presence of pores and cracks. The elements are uniformly distributed in the laser-remelted coating. Nontransformable tetragonal (t′) phase is predominant in the laser-remelted coating with a small amount of cubic phase. Laser remelting greatly enhanced the hardness, wear resistance, and thermal shock resistance of the coatings, and should find more applications.     

3D printing of crack-free high strength Zr-based bulk metallic glass composite by selective laser melting

3D printing of crack-free bulk metallic glasses remains challenge due to the generation of huge thermal stress during the selective laser melting and their intrinsic brittleness. Herein, Zr₅₅Cu₃₀Ni₅Al₁₀ system was selected and 3D printed by selective laser melting technique. The results indicated that bulk metallic glassy composite comprises a large fraction (about 83%) of amorphous phase and minor fraction of intermetallic compounds with free of cracks were successfully fabricated. The 3D printed metallic glassy composite exhibited high strength over 1500 MPa. Experiment combined with finite-element-method simulation not only revealed the mechanism of crystallization at heat affected zones, but demonstrated that low thermal stress reduce the risk of micro-cracks generation and fracture toughness plays a crucial role in suppression the crack propagation during selective laser melting process.     

Influence of remelting on oxidation behaviour and hardness of Sm56Al26Co18 amorphous alloy

The influence of remelting treatment on the oxidation behaviour and the hardness of Sm₅₆Al₂₆Co₁₈ amorphous alloys were investigated by thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction analysis and hardness test apparatus. It was found that the remelting treatment improved the oxidation resistance and hardness of Sm₅₆Al₂₆Co₁₈ amorphous alloy. In addition, the results showed that the oxidation rates of the amorphous ribbons increased as temperature increased, and the hardness of the bulk metallic glassy rods was lower than that of the alloys after annealing.     

Microstructure and Dry Sliding Wear Behavior of Mg-Y-Zn Alloy Modified by Laser Surface Melting

Mg-11Y-2.5Zn alloy was surface-melted using a 6.0 kW continuous wave CO₂ laser as a heat-generating source. X-ray diffractometer, laser optical microscopy, and Vickers hardness indentation were used to characterize the microstructure and hardness of the Mg-11Y-2.5Zn alloy. The results show that the microstructure in the laser-melted zone can be greatly refined and hardness is slightly improved. Dry sliding tests were performed on the as cast and laser surface-melted Mg-11Y-2.5Zn alloys using a pin-on-disk configuration. Coefficients of friction and wear rates were measured within a load range of 20-320 N at a sliding velocity of 0.785 m/s. Laser surface-melted Mg-11Y-2.5Zn alloy exhibited good wear resistance when compared with the as cast one under given applied load conditions, which has been explained by refining of the microstructure in the melted zone. Morphologies of worn surface on the as cast and laser surface-melted Mg-11Y-2.5Zn alloys were examined using scanning electron microscopy. Four wear mechanisms, namely abrasion, delamination, thermal softening, and melting, have operated.     

Wear resistance of laser-clad Ni–Cr–B–Si alloy on aluminium alloy

Using a 5 kW CO₂ laser, two kinds of plasma-sprayed coatings, Ni–Cr–B–Si and Ni–Cr–B–Si+WC alloys, were remelted on aluminium alloy. The wear resistance of both laser-treated samples and plasma-sprayed samples were investigated using a pin-on-disc sliding friction wear tester. A scanning electron microscope (SEM) was used to analyse the abrasion phenomena of the samples and a transmission electron microscope (TEM) was used to study the microstructure of the laser-clad zone. Experimental results showed that the laser-clad samples had double the wear resistance of the plasma-sprayed samples, and that the laser-clad Ni–Cr–B–Si sample exhibited the highest wear resistance. The results of wear surface analysis showed that the microstructure of the alloyed layer of the laser-clad samples was quite compact and the surfaces were also very smooth, and there was less peeling phenomenon of the granules. The microstrucutre of the plasma-sprayed sample was rather loose and there were a lot of granular peelings left on the worn surface. A study of the microstructure showed extensive amorphous and ultra-crystalline structures in the laser-clad zone, to which the increase in hardness and wear resistance may be attributed.     

原位生成 WC-B4C 增强镍基激光熔覆层及其性能研究

目的通过激光熔覆技术,在Q235钢表面原位生成WC-B4C增强镍基熔覆层。方法以WO3,B2O3,C和Ni60混合粉末为预涂原料,采用激光熔覆技术原位生成WC-B4C增强镍基熔覆层,对熔覆层的显微组织和物相构成进行分析,研究其摩擦磨损性能。结果采用合适的工艺参数,通过原位生成WC-B4C形成的增强镍基涂层形貌良好,与基材呈现较好的冶金结合。熔覆层平均硬度1200HV0.3,摩擦磨损失重仅为纯Ni60熔覆层的1/3。结论熔覆层硬度较高,耐磨性很好。大量原位生成的WC-B4C增强相及其均匀分布是熔覆层硬度和耐磨性提高的原因。     

Fretting wear behavior of bulk amorphous steel

Fretting wear of Fe₄₁Co₇Cr₁₅Mo₁₄C₁₅B₆Y₂ bulk metallic glass (BMG) was investigated using the ball-on-disc measurement. The wear behaviors of the samples roughly follow the classical Archard wear law at room temperature. The influence of temperature on wear resistance (R_w) and microhardness (H_v) was evaluated. A good linear correlation was found between R_w and H for the Fe-based BMG. The results indicate that the hardness softening is responsible for the decrease of R_w at high temperature. The wear mechanism at high temperature was elucidated through the analysis of oxidation and debris morphology on the wear scar. Compared with traditional crystalline steels and other non-ferrous metal-based glassy alloys, the bulk amorphous steel shows higher wear resistance and hardness, which promotes its application as an advanced engineering material.     

Microstructure and Mechanical Properties of FeBSiNb Metallic Glass Coatings by Twin Wire Arc Spraying

In this study, FeBSiNb coatings were prepared by twin wire arc spraying process. The microstructure and mechanical properties of as-sprayed coatings were characterized. The results show that the coating is adhering well and very compact with porosity of 1.2% (the value range is 0.9-1.7%). The microstructure of the coating consists of full glassy structure. The crystallization temperature, microhardness, elastic modulus, and average adhesive strength of the coating are 819 K, 16.42 GPa (the value range is 14.38-18.46 GPa), 219 GPa (the value range is 201-237 GPa), and 57.4 MPa (the value range is 55-64 MPa), respectively. The relatively wear resistance of the coating is about three times than that of 3Cr13 martensite stainless steel coating. The reasons for excellent wear resistance of FeBSiNb metallic glass coating are attributed to a uniform amorphous structure, the high ratio of hardness to elastic modulus (H/E) and the ratio of the elastic deformation energy to the total deformation energy (η value). The main failure mechanism of the coating is brittle failure and fracture.     

Microstructure and high-temperature wear behavior of laser clad Ni-Ti-Si ternary metal silicide coatings

Ni-Ti-Si ternary metal silicide coatings were fabricated on AISI 304 stainless steel by laser cladding process. The coatings consisted of Ni₁₆Ti₆Si₇ primary dendrite and interdendritic Fe-Ni-based solid solution γ and exhibited excellent abrasive and adhesive wear resistance under high temperature metallic dry sliding wear conditions. The excellent wear properties were attributed to the high hardness and covalent dominant atomic bond of the metal silicide Ni₁₆Ti₆Si₇. The dominant wear mechanism of the coating were delamination of the coating and material transfer from the mating surface.     

Microstructure and Wear Resistance of Fe-Based Amorphous Metallic Coatings Prepared by HVOF Thermal Spraying

Amorphous metallic coatings with a composition of Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Y₂ were fabricated by means of high velocity oxygen fuel (HVOF) thermal spraying process. The microstructure and wear performance of the coatings were characterized simultaneously in this article. It is found that the coatings present a dense layered structure with the porosity below 1.5%. The coatings primarily consist of amorphous matrix and some precipitated nanocrystals, though a fraction of Fe-rich phases and oxide stringers also formed during deposited process. High thermal stability enables the amorphous coatings to work below 920 K temperature without crystallization. Depending on the structural advantage, the amorphous coatings exhibit high average microhardness of 997.3 HV_0.2, and excellent wear resistance during dry frictional wear process. The dominant wear mechanism of amorphous coating under this condition is fatigue wear, leading to partial or entire flaking off of the lamellae. In addition, the appearance of oxidative wear accelerates the failure of fatigue wear.     

一种新型经济高效非晶涂层的制备与性能表征

利用火焰喷涂技术喷涂自制的气雾化合金粉末取代非晶粉末,制备了NiFeBSiNb非晶纳米晶涂层。分别对粉末和涂层的微观组织结构和热力学性能进行了表征。结果表明,自制的合金粉末球形度较好,大多为球形或椭球形;主要为晶体结构,由Nb₂Ni₂₁B₆晶体相和(Ni,Fe)₂₃B₆固溶体组成。而经过火焰喷涂制备的涂层,形成了非晶相和纳米晶相。通过公式计算此合金体系粉末和涂层形成非晶相的临界冷却速率分别为6.01×10₅K/s和4.56×10₃K/s,解释了在粉末制备过程中较难形成非晶相而喷涂过程中形成非晶结构比较容易。对涂层的摩擦磨损性能进行了测试,涂层摩擦系数仅为0.17,具有优异的耐磨性能。     

Corrosion behavior of Zr-based metallic glass coating on type 304L stainless steel by pulsed laser deposition method

The surface morphology and corrosion behavior of Zr-based amorphous metallic glass (MG) of Zr₅₉Ti₃Cu₂₀Al₁₀Ni₈ alloy and MG coated type 304L stainless steel in different nitric acid media of 1 M, 6 M and 11.5 M HNO₃ is reported. Zirconium based MG of Zr₅₉Ti₃Cu₂₀Al₁₀Ni₈ alloy was successfully deposited on type 304L stainless steel using pulsed laser deposition technique. The SEM morphology revealed a scattered particles of “Donut” shaped features distributed in the amorphous matrix. The atomic force microscope measurement indicated the formation of dense metallic deposited layer of agglomerate of granular clusters with negligible pores or micro-crack in metallic glass coated sample. The results of the potentiodynamic polarization shows that the amorphous MG coated type 304L stainless steel exhibited marginally lower corrosion resistance than MG alloy which is attributed to the presence of corrosion-induced defects in the coated layer. This work reports suitability of using pulsed laser deposition for the preparation of thin film amorphous metallic coating to achieve improved corrosion resistance in nitric acid medium.     

激光熔覆碳化钛增强钛基复合涂层研究进展

钛合金具有密度低、比强度高、耐腐蚀性强等显著优点,在航空航天、海洋工程等领域具有广阔的应用前景。然而,钛合金硬度低、耐磨性差,严重制约其在摩擦工况下的使用寿命。激光熔覆技术具有生产效率高、热影响区窄、结合强度高、组织致密等优势,被广泛用于钛合金零部件表面改性和熔覆修复。高硬、高模量碳化钛的热物性参数与钛合金基材相近,常被选作激光熔覆钛基复合涂层的增强相,以提高其耐磨性。介绍了碳化钛的晶体结构、生长形态和性能特点。综述了碳化钛增强钛基激光熔覆材料体系以及工艺参数对熔覆层成形质量、宏观形貌和微观组织的影响。重点从碳化钛增强相的分布、数量、尺度以及相结构等方面,论述了碳化钛增强钛基激光熔覆层的组织特征,同时阐述了碳化钛强化机制,讨论了碳化钛增强钛基激光熔覆层组织特征与耐磨性能的内在关联性。最后提出了目前激光熔覆碳化钛增强钛基复合涂层研究中存在的问题与展望。