45钢激光合金化后的组织结构及性能

对45钢激光合金化处理可改善其组织结构及性能。研究了45钢不同工艺条件(功率、扫描速度)下激光处理后的组织结构、成分、显微硬度以及耐腐蚀性能。结果表明:45钢合金化后从表层到基体的区域分为合金化区、过渡区和热影响区,其中合金化区由树枝晶和胞状晶组成;合金化区的显微硬度相对于基体有明显提高,且随扫描速度以及功率的增大,合金化区的硬度增大;45钢合金化后耐腐蚀性能得到了较大的提升。     

轮轨试样Co基合金激光熔覆层组织及磨损性能

为提高轮轨材料的耐磨性降低轮轨磨损,利用CO2多模激光器在轮轨试样表面获得Co基合金熔覆层,测试分析了其组织结构性能和显微硬度,利用MMS-2A微机控制摩擦磨损试验机对比研究了激光熔覆处理与未处理轮轨试样的抗磨损性能.结果表明:激光熔覆处理后在轮轨试样表面获得与基体良好结合厚度约1 mm的熔覆层;熔覆层主要由枝晶(γ-Co)和共晶组织(Cr23C6+γ-Co)构成,初生相为γ-Co过饱和固溶体,富含Cr元素,共晶组织中富含Co元素;结合区为粗大柱状晶,从中部到表层出现胞状晶、树枝晶等多种形态.离界面越远组织越细密,组织生长方向紊乱;结合区存在元素扩散,尤其是Fe、Cr和Co含量变化显著;激光熔覆Co基合金后轮轨试样硬度分别提高约52.98%和43.44%,能有效降低对摩副磨损,轮轨抗磨损能力提高约为原来的5倍.     

40Cr激光熔凝硬化组织形态及硬度研究

利用CO2轴流激光加工机对40Cr钢表面进行激光熔凝硬化处理。利用扫描电子显微镜、金相显微镜和显微硬度计研究了不同工艺下熔凝硬化层及基体的显微组织和硬度分布特征。实验表明：熔凝硬化层由熔化区、相变硬化区和热影响区组成;由表及里组织分别为极细隐晶马氏体＋少量残余奥氏体、隐晶马氏体＋碳化物＋残余奥氏体、马氏体＋回火屈氏体＋铁素体。硬化层最高硬度约是基体的3倍;随着扫描速度的增加表层硬度先增加后减小,当扫描速度为2.5m·min^-1时,表层硬度最大,为1097.9HK。     

BT20钛合金表面渗氧研究

氧与钛之间的亲合力比较高,利用这一点可以通过热处理的办法对钛及钛合金部件表面的硬度和耐磨性进行提高.将激光处理的和未经激光处理的BT20钛合金放置在一种特殊固体介质中于大气气氛下进行渗氧处理,来研究炉的加热条件和前处理过程对显微组织和硬度的影响.激光处理过的和未经激光处理的BT20钛合金在相同温度和处理时间的条件下进行渗氧以获得强化层.处理后外层为金红石型的TiO2,里层为由α-Ti组成的氧固溶强化层.激光处理的试样在渗氧后表面硬度最高可达到Hv628,厚度可以达到35μm,而未经激光处理的钛合金的表面硬度最高可以达到Hv580,膜厚度达到25μm .     

硅钢表面激光熔覆高硅涂层对性能的影响

用Nd:YAG脉冲激光在低硅钢表面制备激光熔覆高硅涂层,研究了激光熔覆高硅涂层样品的组织和磁性能.结果表明,制备出的激光熔覆高硅涂层组织致密、无气孔和裂纹,且与基体有良好的冶金结合.经激光熔覆后硅钢表面存在熔覆区、界面结合区和热影响区.熔覆区的显微组织不均匀,随着与结合界面距离的增加,由柱状晶变为树枝晶,最终过渡到表层的细小树枝晶组织.熔覆层与基体之间的结合界面为平面晶组织,热影响区为马氏体组织.熔覆涂层的显微硬度远高于低硅钢基体,其主要原因是涂层具有较高的Si含量,涂层中的α-Fe和γ-Fe双相组织也导致了硬度的提高.激光熔覆高硅涂层硅钢样品经扩散退火后具有室温铁磁性,Si含量的提高使其室温直流磁性能优于原始低硅钢.     

稀土对激光重熔合金化层组织与性能的影响

本文研究了加稀土与不加稀土的Fe-B-Si非晶粉末涂层经激光重熔后的组织与性能。结果发现,加入稀土元素的激光重熔合金化层硬度HV从未加稀土的685提高为1180;磨损体积由未加稀土时的0.86减少到0.42;其硬度、耐磨性均比未加稀土的提高一倍左右。显微组织分析表明,加入稀土的激光重熔合金化层有马氏体相变发生,其基体组织为奥氏体及部分马氏体枝晶、碳化物、合金化合物与奥氏体及马氏体共晶组成。未加稀土的激光重熔合金化层中没有马氏体相变发生,基体组织为奥氏体枝晶和枝晶间的枝杈状、锯齿状、碳化物、合金化合物等共晶组成。     

等离子处理TiO_2纳米粉末对Zn-TiO_2复合镀的影响

为了提高复合电镀层中非金属颗粒的含量,制备出硬度高、耐磨性好的复合镀层。以N2等离子处理纳米TiO2,然后加入电镀锌液中以Zn-TiO2复合电镀为研究对象。研究了电镀的电流效率、镀层硬度以及镀层耐磨性,通过研究得到,等离子处理的TiO2制备的Zn-TiO2复合镀层比未等离子处理TiO2制备的复合镀层显微硬度由165Hv提高到180Hv,耐磨系数由0.75提高到0.9。等离子处理的TiO2在电镀过程中可以提高电镀的电流效率36%以上。     

激光快速重熔对铸造共晶铝合金组织及性能的影响

本文对含稀土铸造共晶铝合金(ZL108)激光重熔组织进行了变时及变温时效处理,与固溶加时效样品相比,激光重熔组织的显微硬度峰值,在HV—H曲线上后移两小时,在HV—T曲线上后移20℃。激光重熔组织比固溶加时效组织具有较好的耐磨性。该两种工艺样品的磨损量随时效时间及时效温度的变化规律与显微硬度随时效时间及时效温度的变化规律完全一致。激光重熔组织细且耐时效,铝枝晶沿 <100> 晶向生长,θ′相沿{100}晶面析出,该θ′相可使显微硬度和耐磨性得到提高。     

铸铁表面激光熔敷镍基合金涂层的耐磨性研究

为了提高铸铁的耐磨性，以35％WC和不含WC的镍基合金粉末为原料对铸铁表面进行激光熔敷处理，利用XRD、SEM、TEM等技术分析了涂层的成分及显微组织结构，并测试了涂层的耐磨性和硬度．结果表明：激光处理后表面迅速熔化和冷却，组织由珠光体 片状石墨组织转化为不同粗细的针状马氏体与残余奥氏体组织；熔敷层的耐磨性和硬度明显提高，且添加35％WC硬质颗粒的熔敷层硬度最高值不在最表层，而在距表面约0．2mm处；合金涂层在磨损机制下表现为犁沟切削、微切削以及硬相质点的剥落，不同基体划痕形式不同。     

激光冲击处理对金属微结构及其性能的影响

论述了激光冲击处理的基本原理,分析了激光诱发的冲击波在材料中的传播过程.激光冲击处理会使金属材料表层发生塑性变形而产生很高的残余压应力;冲击区的显微组织中会产生高密度位错,有时亦有孪晶与相变产生;金属材料表层的塑性变形、高残余压应力、高密度位错、孪晶以及相变,这些因素的共同作用使得金属材料表面硬度、疲劳寿命获得很大的提高.     

Microstructure and Properties of Laser Surface Alloying 304 Stainless Steel with Si

Silicon was added to the surface of 304 stain-less steel by laser melting the sprayed preplaced Sipowders.The optical microscopy,X-ray diffractionand EPMA were employed to investigate themicrostructure and chemical composition of thelaser surface alloyed layer.The hardness of the al-loyed layer was measured by microhardness testand wear resistance was evaluated by scratch test.Corrosion resistance of laser alloyed sample wasstudied in 1N H_2SO_4+0.1N NaCl and0.5N HCl+0.5N NaCl aqueous solutions.Amicrocrystalline intermetallic compound coatingwith smooth surface and good chemicalhomogeneity without porosity and crack is ob-tained.The hardness is about 720 HV.The wear re-sistance is 2 times better than that of the substrate.The corrosion resistance of the laser alloyed sampleis much better than that of 304 stainless steelsample.     

Titanium nitride laser-beam surface-alloying treatment on carbon tool steel

In order to improve the wear resistance of tool steel, a study of TiN surface-alloying treatment on 1% carbon steel by irradiation with a CO₂ laser beam was performed. Argon and nitrogen were used as shielding gases, and their effects on the formation of the surface-alloyed layer were investigated. The effect of cobalt additions to the TiN powder on the hardness of the alloyed layer was also investigated. When argon was used as shielding gas, the depth of the alloyed layer was increased compared with the depth when nitrogen was used as a shielding gas. A portion of the TiN decomposed into titanium in the argon environment, the nitrogen apparently being lost as a gas. The structure of the surface-alloyed layer was composed of a ferritic phase without martensitic structure even at high cooling rates. When this layer was annealed at 1000 ° C for 3 h, part of the titanium precipitated as TiC particles. The hardness of the annealed alloyed layer increased to about 500 Hv. This increase in hardness was accompanied by the appearance of martensite. When nitrogen was used as shielding gas, decomposition of TiN was suppressed and the hardness of the alloyed layer reached 850 Hv. These layers had a martensitic structure. Thus, nitrogen is preferable to argon as a shielding gas if a martensitic structure is desired in this system. When 5% cobalt was added to the TiN powder, the hardness of the alloyed layer increased to 1100 Hv. This increased hardness is caused by stabilization of the martensitic structure caused by an increase in theM _s temperature.     

Microstructural study and wear behavior of ductile iron surface alloyed by Inconel 617

In this research, microstructure and wear behavior of Ni-based alloy is discussed in detail. Using tungsten inert gas welding process, coating of nearly 1–2 mm thickness was deposited on ductile iron. Optical and scanning electron microscopy, as well as X-ray diffraction analysis and electron probe microanalysis were used to characterize the microstructure of the surface alloyed layer. Micro-hardness and wear resistance of the alloyed layer was also studied. Results showed that the microstructure of the alloyed layer consisted of M₂₃C₆ carbides embedded in Ni-rich solid solution dendrites. The partial melted zone (PMZ) had eutectic ledeburit plus martensite microstructure, while the heat affected zone (HAZ) had only a martensite structure. It was also noticed that hardness and wear resistance of the alloyed layer was considerably higher than that of the substrate. Improvement of wear resistance is attributed to the solution strengthening effect of alloying elements and also the presence of hard carbides such as M₂₃C₆. Based on worn surface analysis, the dominant wear mechanisms of alloyed layer were found to be oxidation and delamination.     

Development of wear resistant composite surface on mild steel by laser surface alloying with silicon and reactive melting

The present study concerns laser surface alloying with silicon of mild steel substrate using a high-power continuous wave CO₂ laser with an objective to improve wear resistance. The effect of surface remelting using nitrogen as shrouding environment (with and without graphite coating) on microhardness and wear resistance has also been evaluated. Laser surface alloying leads to formation of a defect free microstructure consisting of iron silicides in laser surface alloyed mild steel with silicon and a combination of silicides and nitrides when remelted in nitrogen. Carbon deposition prior to remelting leads to presence of a few martensite in the microstructure. A significant improvement in microhardness is achieved by laser surface alloying and remelting to a maximum of 800 VHN when silicon alloyed surface is melted using nitrogen shroud with carbon coating. A detailed wear study (against diamond) showed that a significant improvement in wear resistance is obtained with a maximum improvement when remelted in nitrogen atmosphere followed by carbon coating.     

Microstructure and wear resistance enhancement of cast steel rolls by laser surface alloying NiCr–Cr3C2

The laser surface alloying technique was used to form wear resistant layers on 70MnV cast steel rolls with NiCr–Cr₃C₂ powders. The objective was to investigate the effects of the scanning speed on microstructure, phases, microhardness and wear resistance. Results indicate that the alloyed layers had dense, pore and crack free and homogeneous structures, as well as a metallurgical bonding with the substrates. With the increase of scanning speed, volume of retained austenite in the alloyed layer increased, microhardness and wear resistance increased and the microstructure refined. Wear results indicated that the wear resistance of the alloyed layer was enhanced by 7.8 times compared with that of the cast steel substrate. The improvement in wear resistance was attributed to the combined results of the grain refining effect, the solution strengthening effect, the tough γ-Fe matrix of the layer, the distribution of the hard Cr₇C₃, Fe₃C and martensite phases, and the good bonding between these hard phases and the matrix.     

Laser surface coating of Mo–WC metal matrix composite on Ti6Al4V alloy

Laser surface alloying of Mo, WC and Mo–WC powders on the surface of Ti6Al4V alloys using a 2 kW Nd-YAG laser was performed. The dilution effect upon the microstructure, microhardness and wear resistance of the surface metal matrix composite (MMC) coating was investigated. With a constant thickness of pre-placed powder, the dilution levels of the alloyed layers were found to increase with the incident laser power. The fabricated surface MMC layer was metallurgically bonded to the Ti6Al4V substrate. The microhardness of the fabricated surface layer was found to be inversely proportional to the dilution level. The EDAX and XRD spectra results show that new intermetallic compounds and alloy phases were formed in the MMC layer. With the existence of Mo content in the pre-placed powder, the β-phase of Ti in the MMC coating can be retained at the quenching process. With increasing weight percentage content of WC particles in the Mo–WC pre-pasted powder, the microhardness and sliding wear resistance of the laser surface coating were increased by 87% and 150 times, respectively, as compared with the Ti6Al4V alloy. The surface friction of the laser-fabricated MMC coatings was also decreased as compared with the worn Ti6Al4V substrate.     

Enhancement of wear resistance of ductile iron surface alloyed by stellite 6

This paper deals with the improvement of the wear resistance of ductile iron surface alloyed by a hypoeutectic stellite 6 alloy. In this regard, the surface alloyed layer with 3 mm thickness deposited on ductile iron using tungsten inert gas (TIG) surface processing. The microstructure, hardness and wear resistance of surface alloyed layer were investigated using optical microscopy, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis, Vickers hardness (HV0.3) and pin-on-plate tests. The results showed that the microstructure of the surface alloyed layer consisted of carbides dispersed in a Co-based solid solution matrix with dendritic structure. This microstructure was responsible for the improvement of the hardness and wear resistance of the coating. Further investigations showed that the dominant mechanism of the wear in the coated and uncoated samples was delamination wear.     

钛合金表面加弧辉光离子渗镍铬及其性能研究

采用加弧辉光离子渗金属新技术处理钛合金Ti5Al2.5Sn表面,研究了渗层的相组成特点,成分分布情况,评价了改性层的磨擦摩损性能,及与钛合金基体间的接触腐蚀相容性等。结果表明加弧辉光离子渗技术可以快速地在钛合金表面获得NiCr镀渗复合层。渗层由Ni3Ti等金属间化合物组成,其硬度、耐磨性能均高于离子注氮层,具有较高的抗含Cl^-1水溶液腐蚀性能,在含Cl^-1腐蚀环境中与钛合金基体接触相容。     

温度对40Cr13钢等离子表面渗铌层组织的影响

为提高马氏体不锈钢的耐蚀和耐磨性能,选择40Cr13不锈钢为基材、纯铌板为靶材,采用双辉等离子表面冶金技术在不锈钢表面制备合金化层.用SEM、GDOES、XRD等方法分析渗铌温度对铌合金层组织、成分、相组成、表面形貌及硬度的影响,并对渗层形成机制及表面硬化机理进行了研究.结果表明:在900~1 000℃形成的铌合金层组织均匀致密,合金层主要由Nb2C、Nb C、Fe2Nb、Cr2Nb及铌组成;合金层表面粗糙度随渗铌温度的提高而增加;合金层厚度随渗铌温度改变发生不同变化规律,950℃渗铌形成的渗层约13μm,900和1 000℃渗铌后合金层厚度均为7μm左右;不同温度渗铌后试样的表面硬度与基体相比均有较大幅度的提高,1 000℃渗铌后试样表面硬度高达约985 HV0.025,900℃渗铌后约758 HV0.025,而950℃渗铌后表面硬度最低,约698 HV0.025.     

Microstructure and wear properties of Fe–TiC surface composite coating by laser cladding

AISI 1045 steel surface was alloyed with pre-placed ferrotitanium and graphite powders by using a 5-kW CO₂ laser. In situ TiC particles reinforced Fe-based surface composite coating was fabricated. The microstructure and wear properties were investigated by means of scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, as well as dry sliding wear test. The results showed that TiC carbides with cubic or flower-like dendritic form were synthesized via in situ reaction between ferrotitanium and graphite in the molten pool during laser cladding process. The TiC carbides were distributed uniformly in the composite coating. The TiC/matrix interface was found to be free from cracks and deleterious phase. The coatings reinforced by TiC particles revealed higher wear resistance than that of the substrate.