不同Nb含量对(Nb,Ti)C颗粒强化Fe基复合堆焊层微观组织及耐磨性影响研究

目的 颗粒强化金属基复合涂层由于具有优异的力学性能及良好的耐磨性,受到了研究人员的广泛关注,然而,较少有文献报道复合强化相含量与复合涂层力学性能的关系,特别是在电弧堆焊制备的复合涂层中。因此,有必要探明强化颗粒含量对Fe基复合堆焊涂层微观组织及耐磨性的影响规律,为设计新型Fe基复合堆焊材料提供试验依据。方法 通过向药芯焊丝中添加不同含量的Nb,以原位合成(Nb,Ti)C强化相,并据此调控电弧堆焊层中原位生成的(Nb,Ti)C数量密度,进而影响堆焊层的微观组织、硬度及耐磨性。结果 随着Nb的添加,熔覆过程中Nb与基体中的C、Ti反应,原位生成了立方结构的(Nb,Ti)C相,且(Nb,Ti)C相含量随着Nb含量的增加而逐渐增大。与未添加Nb时相比,含质量分数为6% Nb的堆焊层中(Nb,Ti)C复合颗粒的数量密度增加到0.53个/μm²,硬度也由673.08HV0.5增大到734.88HV0.5。摩擦磨损试验结果表明,随着Nb的增加,磨损量呈现出逐渐降低的趋势,其中,Nb含量为6wt.%的堆焊层样品表现出了最浅、最平滑的磨痕,其磨损率仅为1.12×10^?8 mm³/(N.m),磨损机制为轻微的黏着磨损。结论 提高Nb的添加量可以增大(Nb,Ti)C强化相的数量密度,有效提升堆焊层的硬度及耐磨性,并在添加质量分数为6%的Nb时表现出最高的耐磨性能。     

铌在堆焊金属中的应用

利用X射线衍射、TEM、EPMA、SEM等研究了含Nb堆焊金属中的碳化物分布形态及基体组织,分析了碳化物形成过程.结果表明,Nb的加入有利于形成大量碳化物硬质相,但Nb含量过多时,会形成铁素体基体及大量共晶碳化物,导致堆焊金属硬度过低;适量Ti、Nb、V共同作用时,能获得大量均匀分布的颗粒碳化物及马氏体或贝氏体基体,颗粒碳化物是以氧化物为核心的复合碳化物,内层Ti含量高于Nb,外层Nb含量高于Ti.     

Si元素对明弧堆焊奥氏体合金组织及耐磨性的影响

为获得以奥氏体为基体且韧性及耐磨性良好的明弧堆焊合金,采用药芯焊丝自保护明弧焊方法制备了以奥氏体为基体的Fe-C-Mn-Cr-Nb-V-Ti系多元耐磨合金,借助X射线衍射仪、扫描电镜及其附属能谱仪等测试手段,研究了Si含量对其组织和耐磨性的影响。结果表明:堆焊合金基体为γ-Fe,硬质相有(Fe,Cr,Mn,V)_(23)C_6,(Nb,Ti)C和(Fe,Cr)_3(C,B)等;当堆焊合金含1.5%Si(质量分数)时,出现了沿晶(Fe,Cr,Mn,V)_7C_3相;随着Si含量提高,沿晶界分布的(Fe,Cr,Mn,V)_(23)C_6型碳化物数量先增加然后减少,形态从树枝骨架状变为层片状离散孤立分布,胞状γ-Fe晶内原位析出的(Nb,Ti,V)C复合碳化物随之增大,堆焊合金耐磨性呈先提高后下降再提高的趋势;0.9%Si和1.5%Si堆焊合金试样的磨损质量损失低于一般高铬铸铁,具有良好的耐磨性和韧性,其磨损机制主要为磨粒的显微切削。     

镍基合金粉末光束堆焊层的微观组织及强化机理

采用X射线衍射，SEM，EDAX及显微硬度和洛氏硬度等分析手段研究了含碳量为1．0％的NiCrBSi系自熔合金粉末光束堆焊层的微观组织及强化机理，结果表明，采用光束镍基合金粉末堆焊可在铁碳合金表面获得与基体冶金结合良好，无裂纹，轻度稀释的强化层，堆焊热输入对堆焊层稀释率及合金元素烧损的影响程度决定了堆焊层微观组织及物相组成，小热输入堆焊时，堆焊金属经度稀释（η=3.5%），其显微组织由少量初生的γ－Ni和大量的γ－Ni Bi3B Ni3Si三相共晶组成的亚共晶基底，以及在基底上分布着大量的Cr23C6,(Cr,Fe)7C3高硬度相组成，采用大热输入堆焊，堆焊金属稀释率达12％，堆焊层由大量的γ－（Fe,Ni0枝晶和少量γ－(Fe,Ni) M7C3共晶组成，在堆焊层中未发现一次碳化物的析出，在光束粉末堆焊层中大量高硬度M23C6,M7C3共晶组成，在堆焊层中未发现一次碳化物的析出，在光束粉末堆焊层中大量高硬度M23C6，M7C3型碳化物和Ni3B,Ni3Si共晶相的析出以及合金元素在γ相中的过饱和固溶是其是以强化的主要原因，与TIG堆焊相比，采用相近热输入所获得的光束粉末堆焊层的耐磨性能提高了3倍以上。     

冷堆焊高碳Nb-Ti-V系钢质堆焊金属中的碳化物

研究了不同成分的冷堆焊高碳Nb-Ti-V系堆焊金属中碳化物的分布、形态,分析了碳化物在冷焊条件下的形成过程.Nb、Ti可以形成颗粒碳化物,但单独加入且含量较高时,碳化物尺寸过大,对基体固溶强化较弱,堆焊金属硬度过低;单独加入V时则形成了网状碳化物;适量Nb、Ti、V同时加入,获得了均匀分布的颗粒碳化物及强韧的基体,堆焊金属耐磨性优于D317的堆焊金属.     

钛合金表面Nb-C复合渗层摩擦磨损性能的研究

为提高钛合金表面的耐磨性能,采用等离子表面合金化技术在Ti6A14V(TC4)合金表面形成含Nb的梯度改性层,然后进行渗C复合处理,得到Nb-C复合改性层,研究了改性层的显微组织形貌、成分分布、相结构特征及硬度分布,并进行了球盘摩擦磨损实验.结果表明,Nb、C元素呈梯度分布,合金层主要由Ti、TiC、Nb2C、NbC等...     

WC颗粒在堆焊过程中溶解机理的研究

研究了WC／Ni3Al表面强化功能复合材料的制备及WC颗粒的溶解机理。在堆焊过程中，WC／Ni3Al复合材料焊条中的WC直接溶解进入基体中，然后析出W2C，而非WC分解成W2C然后溶解。当焊条中含5％(质量分数)WC时，部分Al被氧化，WC溶解，析出W2C，形成碳化物包裹氧化物的球形复合析出物，基体转化成Nb(AlTi)C，形成碳化物包裹氧化物／金属间化合物的复合材料。随着WC含量增加，Al氧化减少。当焊条中的WC含量达到30％时，焊层中的Al不被氧化，表面层中的大部分WC颗粒溶解，析出针状W2C，形成碳化物／金属间化合物复合材料，耐磨性可达45钢的3倍以上。     

原位复合(Nb-Cr-Ti)C堆焊金属的组织与性能

工业机械设备表层磨损失效非常普遍,堆焊是其最有效的保护方法之一.采用自制焊条,通过对堆焊合金的组织结构设计和成分调整,自行设计了Nb-Cr-Ti系堆焊金属,并堆焊出了耐磨抗裂的合金层.采用光学显微镜、扫描电镜、能谱分析仪器以及磨损试验机等,分析了堆焊层组织结构和性能,探讨了各合金元素在堆焊层中的作用.结果表明:堆焊层组织为混合型马氏体和少量残余奥氏体+弥散分布的复合(Nb-Cr-Ti)C颗粒,低碳马氏体和高碳马氏体数量相当.铌在高温下先析出生成硬质相NbC,碳化物硬质点呈颗粒状弥散分布,使组织细化,也使焊层达到较高的硬度,提高了耐磨性.碳化物的大量弥散析出,使得基相含碳量较低而转变成低碳马氏体,因基相有较高的塑韧性,抗裂性增强.该堆焊层的耐磨性和抗裂性明显优于商用D667焊条.     

Cr8Nb3CSiMnTi系堆焊合金的组织及耐磨性研究

为解决中铬合金耐磨性不足的问题，采用“复合粉粒+H08A实心焊丝”埋弧焊方法制备Cr8Nb3CSiMnTi系中铬耐磨合金，借助X射线衍射仪(XRD)、扫描电镜(SEM)及附属能谱仪(EDS)等手段，研究了碳含量对该合金组织和耐磨性的影响。结果表明：中铬堆焊合金的基体由α-Fe构成，硬质相包括(Fe, Cr)₇C₃、(Fe, Cr)₃C碳化物和(Nb, Ti)C等相；随着碳含量升高，α-Fe固溶的铬含量持续减小，沿晶(Fe, Cr)₇C₃型碳化物数量增多，形态从孤立状依次改变为树枝状、定向聚集态等，与(Nb, Ti)C相的间距随之减小。湿砂橡胶轮式磨损试验结果显示，随碳含量提高，堆焊合金的耐磨性先显著改善然后降低，这主要与沿晶碳化物(Fe, Cr)₇C₃数量提高以及其与(Nb, Ti)C相的间隔距离改变有关；堆焊合金的韧性则先持续下降，然后上升，这不仅决定于基体数量，而且与沿晶碳化物的形态及其分布有关；其磨损机制包括显微切削和剥落，以显...     

316H堆焊UNS N10003合金参数优化、组织和硬度的研究

研究异种合金焊接可以降低熔盐堆结构材料的成本并确保其安全性,本文采用钨极氩弧焊(GTAW)工艺,在316H不锈钢表面堆焊一层耐高温熔盐腐蚀的UNS N10003合金,优化了焊接工艺参数,通过光学显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、维氏硬度计等研究了堆焊层及界面的形貌、组织和硬度,为进一步研究多层、多道堆焊提供理论依据。研究结果表明:当电流一定时,稀释率随送丝速度的增加而减小,堆焊层高度随送丝速度的增加而增加,当送丝速度一定时,改变电流大小,堆焊层高度的变化范围为0.2~0.5 mm。堆焊层界面处可以细分为对流混合区(WM)、非对流混合区(UZ)和热影响基体区(BM)。堆焊层主要为奥氏体组织,在WM区有大量富Mo的M2C碳化物析出,UZ区的析出相主要是δ铁素体;316H基体区和WM区硬度分别为(160±10)HV和(202±11)HV,在γ基体的枝晶界上分布着尺寸细小的骨架状碳化物导致WM区硬度升高。     

Effects of Alloying Elements on Microstructure and Erosion Resistance of Fe—C—Cr Weld Surfacing Layer

Effects of alloying elements on microstructure and erosion resistance of Fe-C-Cr weld surfacing layer have been studied. The experimental results show that increasing C and Cr content favors improving the erosion resistance of the layer, and the excessive C and Cr result in decreasing the erosion resistance at 90 deg. erosion. That Mo, Nb or Ti improves the erosion resistance of Fe-C-Cr weld surfacing layer is mainly attributed to increasing the amount of M7C3 and forming fine NbC or TiC in austenite matrix, but the excessive Mo, Nb or Ti is unfavorable. The addition of Mo, Nb and Ti in proper combination possesses stronger effect on improving the erosion resistance and the erosion resistance (εA) of Fe-C-Cr weld surfacing layer with fine NbC, TiC and M7C3 distributing uniformly in austenite matrix obviously increases to 2.81 at 15 deg. erosion and 2.88 at 90 deg. erosion when the layer composition is 3.05C, 20.58Cr, 1.88Mo, 2.00Nb and 1.05Ti (in wt pct).     

Mechanical and wear behavior of alloyed gray cast iron in the quenched and tempered and austempered conditions

Three groups of hypereutectic cast irons alloyed with Cu, Ni and microalloying additive like Ti and Nb were examined for its hardness and wear resistance in the austempered (360 °C/3 h) and quenched and tempered conditions at varying tempering temperatures. It is observed that the cast irons in the quenched and tempered condition showed good wear resistance and moderate hardness at 400 °C. This was comparable with the wear resistance in austempered condition. The study also showed that in quenched and tempered condition, increasing Cu content in cast irons improved its wear resistance moderately while increasing Ni content has decreased its wear resistance. The presence of strong carbide formers (Nb, Ti) did not give significant improvement in wear resistance in quenched and tempered condition. Even in austempered alloys, higher Cu content increases its wear resistance and higher Ni content decreases their wear resistance. The austempered alloys showed ausferritic microstructure with 20% austenite phase which enhances wear resistance through transformation induced plasticity effect. On the other hand, the quenched and tempered alloys showed good wear resistance at 400 °C due to fine tempered carbides in the matrix.     

Effect of simultaneous addition of ferroniobium and ferrotitanium on properties of hardfacing

The slag-free self-shielded flux-cored wire with simultaneous addition of ferroniobium (Fe-Nb) and ferrotitanium (Fe-Ti) was developed to fabricate the iron-based hardfacing alloys. The transfer coefficients of Nb and titanium of slag-free self-shielded flux-cored wire were 91.2 and 63.8%, respectively. The changes in microstructures indicate that Nb and Ti addition shifted the carbon concentration in the remaining liquid to one corresponding to the near eutectic state owing to the formation of (Nb, Ti)C which consumed carbon. The wear loss of the hardfacing alloy with 18?wt-% Fe-Nb and 6?wt-% Fe-Ti addition was the smallest among all the alloys owing to the formation of reinforced uniform quadrangle-shaped (Nb, Ti)C carbides in the refined microstructure and the highest hardness.     

Fabrication of in situ TiC locally reinforced manganese steel matrix composite via combustion synthesis during casting

In situ TiC particulates locally reinforced manganese (Mn) steel matrix composite was successfully fabricated via combustion synthesis of (Fe,Ti)–C system during casting. XRD results reveal that the phases of the composites consist of TiC, α-Fe and austenite. Microstructure of the locally reinforced manganese (Mn) steel matrix composite consists of three separate regions, i.e. a TiC particulate-reinforced region, a transition region, a steel matrix region. TiC particles in the reinforced region, having fine size of 2 μm, are distributed uniformly. The hardness and wear resistance of the TiC particulates locally reinforced composites are much higher than those of quenched Mn13 steel. Furthermore, the microstructure formation mechanism of the composite was discussed.     

Wear resistance of laser-deposited boride reinforced Ti-Nb–Zr–Ta alloy composites for orthopedic implants

The inherently poor wear resistance of titanium alloys limits their application as femoral heads in femoral (hip) implants. Reinforcing the soft matrix of titanium alloys (including new generation β-Ti alloys) with hard ceramic precipitates such as borides offers the possibility of substantially enhancing the wear resistance of these composites. The present study discusses the microstructure and wear resistance of laser-deposited boride reinforced composites based on Ti–Nb–Zr–Ta alloys. These composites have been deposited using the LENS™ process from a blend of elemental Ti, Nb, Zr, Ta, and boron powders and consist of complex borides dispersed in a matrix of β-Ti. The wear resistance of these composites has been compared with that of Ti–6Al–4V ELI, the current material of choice for orthopedic femoral implants, against two types of counterfaces, hard Si₃N₄ and softer SS440C stainless steel. Results suggest a substantial improvement in the wear resistance of the boride reinforced Ti–Nb–Zr–Ta alloys as compared with Ti–6Al–4V ELI against the softer counterface of SS440. The presence of an oxide layer on the surface of these alloys and composites also appears to have a substantial effect in terms of enhanced wear resistance.     

Wear properties of Ti–13Zr–13Nb (wt.%) near β titanium alloy containing 0.5 wt.% boron in dry condition,Hank's solution and bovine serum

The effect of heat treatment on the microstructure, hardness and sliding wear behaviour of Ti–13Zr–13Nb (wt.%) containing 0.5 wt.% B (TZNB) has been studied and compared with that of Ti–13Zr–13Nb (wt.%) (TZN) alloy. The wear properties were tested in dry condition and in simulated body fluid (Hank's solution and bovine serum) to understand the effect of different medium on wear behaviour of the TZNB alloy. Depending on the heat treatment condition the microstructure of the alloy consisted of α/martensite and TiB in β matrix. In general, the hardness of all the heat treated samples varied in a narrow range and in most of the cases addition of boron to the TZN alloy decreased the hardness. Almost all cases, no significant variation of the wear rate in dry condition with heat treatment was observed. Compared with the wear rate in dry condition, the wear rate in Hank's solution of the all the TZNB samples increased substantially. Moreover, the wear was found to be most severe in bovine serum. Addition of boron to TZN alloy did not result in any improvement in the wear resistance in all the media studied.     

Ti particle-reinforced surface layers in Al: Effect of particle size on microstructure,hardness and wear

Two types of Ti particles are used in an ultrasonic impact peening (UIP) process to modify sub-surface layers of cp aluminium atomized, with an average size of approx. 20 μm and milled (0.3–0.5 μm). They are introduced into a zone of severe plastic deformation induced by UIP. The effect of Ti particles of different sizes on microstructure, phase composition, microhardness and wear resistance of sub-surface composite layers in aluminium is studied in this paper. The formed layers of a composite reinforced with smaller particles have a highly misoriented fine-grain microstructure of its matrix with a mean grain size of 200–400 nm, while reinforcement with larger particles results in relatively large Al grains (1–2 μm). XRD, SEM, EDX and TEM studies confirm significantly higher particle/matrix bonding in the former case due to formation of a Ti₃Al interlayer around Ti particles with rough surface caused by milling. Different microstructures determine hardness and wear resistance of reinforced aluminium layers: while higher magnitudes of microhardness are observed for both composites (when compared with those of annealed and UIP-treated aluminium), the wear resistance is improved only in the case of reinforcement with small particles.