电子束淬火与渗氮的复合热处理技术

复合热处理,也称作双重或混合技术,提供了具有新的组织／性能关系的基体化合物层,而处理工序是关键。这种技术能达到单项处理工艺或单项工艺的简单叠加所不能达到的性能和性能梯度化学热处理与高能柬表面淬火特别是电子束淬火相结合,使这项技术取得了显著进展。本文在评述热化学与热（表面）处理技术相结合的历程（重大事件）后,介绍了渗氮后进行电子束淬火和电子柬淬火后进行渗氮的原理及其对微观组织与性能的影响,并讨论了典型的工业应用实例、该领域的进一步发展主要是高能束（电子束或激光束）淬火与硬质涂层技术相结合．     

Electron meets nitrogen: combination of electron beam hardening and nitriding

Abstract

Combined heat treatments, also known as duplex or hybrid technologies, offer new structure/property relationships in layered matrix compounds. The treatment sequence is critical. There are within reach both properties and property gradients that are impossible to achieve using the respective single treatment processes alone nor by simple addition of the effects of the single processes. Good technical progress is given by the combination of thermochemical treatment with high energy beam surface hardening, in particular electron beam hardening. After a historical survey (milestones) of the combination of thermochemical with thermal (surface) heat treatment technologies, the paper deals with the principles of the combining electron beam hardening after nitriding and vice versa , electron beam hardening before nitriding and the effects on microstructure and properties. Typical examples of industrial application are discussed. In this field of heat treatment, further development is focused on combinations of high energy beam hardening (electron or laser beam) with hard coating.     

Substrate Strengthening of CVD Coated Steels

CHEMICAL VAPOR DEPOSITION is successfullyused in production since decades to enhance the wearresistance of tools.Excellent coating properties areachieved with relatively simple equipment.The highdeposition temperatures used for CVD favor a goodadhesion of CVD coatings on the substrate,but alsonegatively influence the properties of the steelsubstrates.High coating temperatures followed byrelatively low cooling rates demand a subsequent heattreatment to restore the properties of the s…     

Characterization of laser treated steels using instrumented indentation by cylindrical flat punch

The aim of the present work is to assess the possibility of predicting the thickness of the hardened layers produced by High Power Diode Laser (HPDL) heat treatment. Instrumented indentation by cylindrical flat punch was carried out in order to evaluate the effectiveness of the surface-hardening heat treatments on milled AISI 1040 steel substrates by varying laser operational parameters as well as the morphology of steel substrates. In particular, the trend in load-penetration depth were obtained, supporting the identification of the depth at which the hardened layer starts transferring the deformation to the softer substrate, that is, the Critical Transition Depth (CTD) in addition to identifying the overall degree of hardening reached by the laser treated material. On the other hand, hardness profiles and the thickness of hardened layers were also monitored by using combination of Vickers micro-hardness tests and standard metallographic characterizations.Analytical examinations and simple mathematical simulations of the experimental results coming from indentation tests and conventional testing procedures showed good correlation between the extent of the heat affected zone (HAZ), hardness and CTD. In conclusion, this study demonstrates that indentation tests are an effective, sensitive, fast, and low-cost characterization technique for heat treated steels.     

Fatigue behavior of duplex treated TiCxN1−x- and Ti1−xAlxN-hard coating steel compounds

Recently, modified surface treatment methods for cutting tools were developed combining a heat treatment and a subsequent hard coating (duplex treatment). As a consequence, the wear resistance has been improved considerably. As fatigue is an important failure mechanism during application, the present paper focuses on the improvement of the fatigue behavior by an optimization of heat treatment and hard coating. The problem is approached in two steps: first, the fatigue behavior of high-speed tool steel S6-5-2 is investigated, surface-treated with different plasma heat treatments (plasma nitriding and -carbonitriding). The results on bending fatigue testing indicate the superiority of plasma nitriding compared with both plasma carbonitriding and untreated substrate. Hence, in a second step the plasma nitrided tool steel is coated with PACVD hard coatings of the system Ti-Al-C-N and the fatigue behavior of these hard coating steel compounds is investigated. Obviously, the type and stoichiometry of the hard coating influence the fatigue behavior of the compound. For TiC_xN_1−x films, the fatigue strength increases with increasing carbon content, whereas for Ti_1−xAl_xN-films, the fatigue strength decreases with increasing Al content. While for an optimized hard coating the fatigue behavior of the compound is superior to hardened non-nitrided steel, no significant improvement was found as compared with plasma nitrided steel.     

Post-treatment of thermal spray coatings on magnesium

Magnesium alloys have a beneficial combination of high strength to weight ratio, good machinability and high recycling potential. Despite this, the application of magnesium still is behind that of other constructive materials mainly due to low wear and corrosion resistance. For more demanding applications, a large amount of surface treatment methods are developed to overcome this problem. Thermal spraying is an efficient and flexible method of coating deposition and is widely used for protection of different materials against corrosion and wear. Nevertheless, the bonding of thermal spray coatings on magnesium alloys is not sufficient, so the following post-treatment processes are needed. One of such possibilities is high energy beam treatment of thermally sprayed coatings. During the heat treatment of magnesium substrates with coating the remelting of coating and a thin surface layer of substrate occurs. Depending on the combination of applied coating system and treatment method, different processes can be realised in modified layers: the alloying of magnesium substrate with other elements to improve corrosion properties, redistribution of hard particles from composite coating and new phases formation during the processing to improve the wear resistance of magnesium alloys. In the present work some examples concerning the laser and electron beam treatment of aluminium based composite coatings as well as infra red irradiation of zinc based coatings are described. Coatings are deposited on magnesium substrates (AM20, AZ31, AZ91) by arc spraying with Zn, ZnAl4 and ZnAl15 solid wires and cored wires in aluminium core with powder filling containing different hard particles, such as boron, silicon and tungsten carbide or titanium oxide. Remelting of thermal spray coatings is carried out by means of continuous irradiation of СО₂-laser in nitrogen or argon atmosphere, electron beam in vacuum and focused tungsten halogen lamp line heater in atmosphere. Microstructure of sprayed coatings as well as that of modified surface layers is investigated by metallographic methods. Corrosion properties are estimated by electrochemical measurements. Abrasion wear resistance of the modified layers is determined by scratch test, corundum grinding disk test and Rubber wheel test. It is shown that all methods applied for processing of thermal spray coatings lead to formation of modified surface layers in magnesium substrate with improved wear and corrosion properties. Different mechanisms of microstructure formation such as redistribution of chemical composition of composite coating components, partial remelting of hard phase particles, and new phases formation are discussed. Electrochemical behaviour of modified surface layers is mostly improved due to alloying, homogenization of element distribution and strong decrease of as-sprayed coating porosity. Abrasion wear resistance of processed magnesium substrates strongly depends on the microstructure and usually is 5 to 20 times higher compared with base material.     

Effect of a laser pre-quenched steel substrate surface on the crack driving force in a coating–steel substrate system

A mechanical model of a coating/laser pre-quenched steel substrate specimen with a crack oriented perpendicular to the interface between the coating and the hardened layer is developed to quantify the effects of the residual stress and hardness gradient on the crack driving force in terms of the J-integral. It is assumed that the crack tip is in the middle of the hardened layer of the pre-quenched steel substrate. Using a composite double cantilever beam model, analytical solutions can be derived, and these can be used to quantify the effects of the residual stress and the hardness gradient resulting from the pre-quenched steel substrate surface on the crack driving force. A numerical example is presented to investigate how the residual compressive stress, the coefficient linking microhardness and yield strength and the Young’s modulus ratio of the hardened layer to the coating influence the crack driving force for a given crack length.     

Laser transformation hardening on rod-shaped carbon steel by Gaussian beam

Laser transformation hardening(LTH) is one of the laser surface modification processes. The surface hardening of rod-shaped carbon steel (SM45C) was performed by lathe-based laser composite processor with Gaussian-beam optical head. The LTH characteristics by dominant processes, longitudinal and depth directional hardness distributions and behaviors of phase transformation in hardened zones were examined. Especially, two concepts of circumferential speed and theoretical overlap rate were applied. When laser power increased or circumferential speed decreased, the surface hardening depth gradually increases due to the increased heat input. Moreover, the longitudinal hardness distribution particularly shows periodicity of repetitive increase and decrease, which results from tempering effect by overlap. Finally, the feasibility of laser transformation hardening is verified by using the beam with Gaussian intensity distribution.     

过丝辊激光表面淬火

用连续波CO2激光束对4Cr13不锈钢过丝辊进行激光表面淬火。研究了淬火层的显微组织及硬度分布，探讨了用激光表面淬火技术替代传统的热喷涂处理的可能性。结果表明，激光表面淬火硬化层的硬度和硬度深度均可达到甚至超过热喷涂涂层的硬度和硬度深化，用激光表面淬火技术替代传统的热喷涂对过丝辊进行表面强化处理是可行的。     

Influence of laser hardening and resulting microstructure on fatigue properties of carbon steels

Cylindrical specimens of a CSN 12050 carbon steel, equivalent to the UNS G 10420 steel, with two different initial microstructures, normalized and heat treated, were surface processed without melting by a 2.5 kW, CO₂ laser to study the effects of laserbeam hardening and resulting microstructure on fatigue properties and mechanisms. Two configurations of circumferential laser passes were made, resulting in one and three separate surface hardened lines, respectively. Fatigue resistance was studied using alternating bend tests. A detailed metallographic study and x-ray measurements of surface stresses were carried out. It was shown that the laser beam hardening under different conditions either reduced or slightly improved the fatigue life.     

激光熔敷NiTi/Ni3Ti金属间化合物复合材料涂层组织及耐磨性

以Ni79Ti21（wt％）合金粉末为原料，采用同步送粉激光熔敷技术在BT20钛合金表面制备出NiTi／Ni3Ti金属间化合物复合材料涂层，分析了该涂层的显微组织，测试了该涂层的室温干滑动磨损性能。结果表明，激光熔敷涂层组织均匀致密，与基材呈良好的冶金结合，具有优良的抗滑动磨损性能。     

Laser densification of organic coating: Effects of laser wavelength,operating parameters and substrate properties

Mechanical bonding and interface behaviour play a key role for any materials deposited on different substrates. Usually, a post-spray heat treatment is required to improve the coating morphology and to enhance mechanical properties of thermal-sprayed polymeric coating. The effects of YAG, CO₂ and diode laser radiations on as-sprayed PEEK coating deposited on stainless steel and aluminum substrates were investigated. The results revealed a good coating densification and interface behavior. A correlation between coating and substrate absorption coefficients, their thermophysical properties and laser operating parameters was shown. Besides, the finite element modeling based on IR temperature measurements during diode laser irradiation demonstrated that the densification of organic coating occurs above its melting point.     

Hard coatings on thermochemically pretreated soft steels: application potential for ball valves

The combination of a thermochemical heat treatment (e.g., nitriding or carburizing, with or without plasma enhancement) and a hard coating [e.g., titanium nitride (TiN), chromium nitride (CrN) or amorphous hydrogenated carbon (a-C:H)] is known as “duplex treatment”. It offers the possibility to improve the functional properties of tools and machine parts compared with a single treatment. The combination of plasma nitriding and physical vapour deposited hard coating has been investigated by various groups, mostly for increasing the wear resistance of tools. However, machine parts and precision components are also very promising candidates for duplex treatments, especially when they are made of soft steels such as stainless steels. This paper shows that the functional behaviour of duplex-treated parts is determined both by the application-oriented optimization of the thermochemical heat treatment and by selection of the appropriate hard coating. The hard coatings include TiN, chromium-containing amorphous hydrogenated carbon (a-C:H:Cr) and “pure” a-C:H. For demonstration purposes, this paper focuses on the ferritic stainless valve steel X20Cr13.     

Effect of h-BN addition on the properties of nanostructured Al2O3-TiB2-TiN based coatings developed by combined SHS and laser surface alloying

A hard coating was obtained on AISI1025 steel substrate by the action of a high power laser beam on a powder mixture of Al, TiO₂ and h-BN pre-placed on the substrate surface. The precursor powder mixture underwent self-propagating high-temperature synthesis (SHS) at the high temperatures induced by the incident laser. The products of SHS were subsequently laser alloyed onto the substrate, whereby, a hard, nanostructured coating was formed comprising of Al₂O₃, TiB₂ and TiN. Excess h-BN in the precursor resulted in the presence of free h-BN in the coating. Microhardness and coefficient of friction (with WC-Co as counterbody) of the coating were found to reduce with increase in h-BN content in the precursor. It was possible to develop a coating with a property combination of high hardness, low wear rate and low friction coefficient.     

Modeling the Influence of Process Parameters and Additional Heat Sources on Residual Stresses in Laser Cladding

In laser cladding thermal contraction of the initially liquid coating during cooling causes residual stresses and possibly cracks. Preweld or postweld heating using inductors can reduce the thermal strain difference between coating and substrate and thus reduce the resulting stress. The aim of this work is to better understand the influence of various thermometallurgical and mechanical phenomena on stress evolution and to optimize the induction-assisted laser cladding process to get crack-free coatings of hard materials at high feed rates. First, an analytical one-dimensional model is used to visualize the most important features of stress evolution for a Stellite coating on a steel substrate. For more accurate studies, laser cladding is simulated including the powder-beam interaction, the powder catchment by the melt pool, and the self-consistent calculation of temperature field and bead shape. A three-dimensional finite element model and the required equivalent heat sources are derived from the results and used for the transient thermomechanical analysis, taking into account phase transformations and the elastic-plastic material behavior with strain hardening. Results are presented for the influence of process parameters such as feed rate, heat input, and inductor size on the residual stresses at a single bead of Stellite coatings on steel.     

汽车车门用高强防撞杆在高频淬火加热中的组织转变

研究了国产BR1500HS高强钢制汽车车门防撞杆的高频感应淬火工艺,探究了在不同的进给速度下(70~120 mm/s),防撞杆获得完全淬透组织时的加热电压与进给速度的关系曲线图。结果发现,加热电压随进给速度的降低,淬透所需的加热电压也降低,并以分界线的形式区分是否完全淬透。防撞杆高频感应淬火采用分界线以上30 V的加热电压范围,其力学性完全能满足汽车主机厂的性能要求。     

激光相变强化工艺参数对40CrNiMo钢组织与耐磨性的影响EI北大核心CSCD

航空发动机传动部件服役过程易磨损失效,为提高其寿命和可靠性需进行表面强化。在40Cr Ni Mo合金钢表面进行激光相变强化处理,通过调控扫描速度获得不同激光相变强化区组织,对其显微硬度和摩擦磨损性能进行表征。结果表明,随扫描速度降低,硬化层宽度和深度增大,显微组织变粗,马氏体含量增加。不同扫描速度下,硬化层表面显微硬差异小,为77~789 HV,相比基材(330 HV)提升135%以上。激光相变强化处理后,试样耐磨性大幅提升,硬化区组织为孪晶马氏体+回火索氏体的试样耐磨性最优,摩擦因数相比基材降低24.9%,磨损体积减少94.3%。研究表明,由高强的细小孪晶马氏体和韧性较好的细小回火索氏体组成的复相组织,能有效阻碍裂纹形成和扩展,显著提升耐磨性能。调控激光相变强化工艺参数,获得高强马氏体+韧性相的复相组织,能获得优异的耐磨性能。     

40CrNiMoA钢激光相变硬化技术

研究了40CrNiMoA钢激光淬火工艺参数与硬化层深度及硬度之间的相互关系，以及淬硬层微观结构特征。结果表明，随着光斑扫描速度的提高，硬化层深度降低，表面硬度存在一个极大值；随着激光功率的升高，硬化层深度增加，表面硬度也存在一个极大值，激光淬火硬化层依其组织特征，分为完全淬硬区，过渡区及高温回火区。     

AISI1045钢表面激光熔覆FeCoCrNiAl0.5Ti0.5涂层的界面特性及摩擦性能

激光熔覆高熵合金涂层摩擦磨损行为的研究主要聚焦在涂层表面,鲜有对熔覆层/基体界面区域的摩擦学行为进行研究。为了提高AISI 1045钢的耐磨性,采用激光熔覆技术在AISI 1045钢基体表面制备宏观形貌良好、组织均匀的FeCoCrNiAl_0.5Ti_0.5高熵合金涂层。利用OM、XRD、SEM、EDS和摩擦磨损测试仪对激光熔覆FeCoCrNiAl_0.5Ti_0.5涂层的微观结构、物相组成、界面特性和摩擦磨损性能进行研究。通过对FeCoCrNiAl_0.5Ti_0.5涂层XRD图谱和元素分布分析发现,涂层主要由面心立方(Fe,Ni)相和体心立方相(BCC)形成的共晶组织及其中弥散分布着的Ni Al金属间化合物构成。硬度测试表明,从涂层顶部到基体,涂层、稀释区、热影响区和基体的平均显微硬度分别为518±20、561±63、473±81和217±12 HV0.2。涂层/基体界面区域生成了Cr₂₃C₆,在摩擦过程中会形成一层摩擦...     

45钢激光相变硬化组织及性能研究

    利用轴流CO₂激光加工机对45钢在轴流基模条件下进行激光相变硬化处理,并研究了其激光相变硬化组织及性能.结果表明,改性层微观组织由表层至基体依次为：表面熔凝区为片状马氏体,均匀相变硬化区为隐晶马氏体,过渡区为混合马氏体、屈氏体和部分未熔的铁素体;激光相变硬化改性层的硬度与基体相比有大幅度提高;最高硬度（约为基体的3倍）出现在次表层;激光相变硬化处理后耐蚀性有所提高,随扫描速度增加,耐蚀性增强.