回火马氏体中合金碳化物的3D原子探针表征Ⅰ.形核

Nb-V微合金钢在1200℃固溶0.5 h后淬火,在450℃回火不同时间,用三维原子探针(3DAP)研究了回火过程中合金碳化物的形核规律.结果显示,淬火态Nb-V微合金钢在450℃回火时合金碳化物处于形核阶段,合金元素可通过动态再分配,实现渗碳体到合金碳化物的原位转变,或者在位错等缺陷处直接与C结合,完成合金碳化物的单独成核长大,或者偏聚在残余奥氏体/基体和未溶的AlN粒子/基体界面处,实现合金碳化物的异质形核长大.     

高硬度钢焊缝第二相的强化及增韧

研究了在Ｎｂ,Ｔｉ,Ｚｒ,Ｖ和ＲＥ共存的高碳焊缝中碳化物和基体组织的特点及对韧性的影响。结果表明,多元强碳化物元素与ＲＥ的综合作用,可诱使碳化物早期大量弥散析出。析出过程发生在焊缝凝固之前,同核心多维析出是碳化物由液相直接析出的主要机制;强碳化物元素与碳符合比规律,可导致基体“贫碳”而转变为板条马氏体（Ｍ１）,最终获得以碳化物强化为主的高硬度兼高韧性焊缝。     

Effect of Ti-V-Nb-Mo addition on microstructure of high chromium cast iron

The effects of trace additions of multi-alloying elements (Ti,Nb,V,Mo) on carbides precipitation and ascast microstructure of eutectic high chromium cast iron containing 2.85wt.％C and 31.0wt.％Cr were i...     

Effects of alloy elements on microstructure and crack resistance of Fe-C-Cr weld surfacing layer

0　IntroductionFe C Crsurfacingalloysarewidelyusedinindustries ,mainlyduetotheirhighwearresistance .Underconditionsofabrasiveenvironments,theeffectofcompositionandmi crostructureontheabrasionresistancehasbeenextensivelystudied[1～4 ] .TheauthorsalsoevaluatederosionresistanceofFe C Crweldsurfacinglayersbecausealargenumberofma chinecomponentssufferedfromsevereerosion ,suchasper cussiveplate ,rotorbladeandexhaustpipe ,etc .However,thelowcrackresistanceofFe C Crweldsurfacinglayershasbecomethei…     

Combination of TEM and 3D atom probe study of microstructure and alloy carbide in a Nb-V micro-alloyed steel tempered at 650 °C

3D atom probe (3DAP) combined with TEM is applied to characterize the nanostructure and composition of coarsening carbides that precipitate in a Nb-V micro-alloyed steel tempered at 650 °C for 4 h. The results indicate that high temperature tempering of the as-quenched lath-like martensitic structures leads to the coarsening of alloyed carbide in the recovered ferritic matrix. TEM characterization and EDS analysis show that the alloy carbides are typically spherical or ellipsoidal and are enriched with V, Nb and Mo. Crystallographic lattice overlap and distortion create a distinct optical Moiré pattern at the carbide/matrix boundary, as observed by HRTEM. 3DAP gives the compositional distribution at atomic scale in the coarsening carbide and the surrounding matrix. Non-carbide-forming elements such as Si and Al are depleted in the carbide and are enriched at the carbide/matrix heterophase interface. Carbide-forming elements such as Mn, V, Mo and Nb distribute heterogeneously in the whole carbide, leading to the formation of a Mn-, V- and Mo-enriched core and Mo-enriched external shell.     

Nucleation and thermal stability of carbide precipitates in high Nb containing TiAl alloys

This work monitors the nucleation, growth and coarsening of carbides in powder metallurgically processed, high Nb containing TiAl alloys. The effects of carbon content, annealing conditions and internal defects on the precipitation and stability of carbides were systematically investigated by high energy X-ray diffraction and transmission electron microscopy. In general, at 800 °C the carbide microstructure can still change significantly up to 1000 h of annealing. It is found that a higher carbon concentration promotes the carbide precipitation process and increases the thermal stability of carbides. Internal interfaces and other crystallographic defects act not only as heterogeneous nucleation sites for perovskite Ti₃AlC carbides but also as carbon sinks. This retards the carbide nucleation in the interior of γ-TiAl grains. By homogenising the carbon distribution through solution heat treatment the nucleation of carbides in the γ-TiAl matrix is significantly accelerated as an effect of higher matrix carbon content.     

回火马氏体中合金碳化物的3D原子探针表征Ⅲ.粗化

Nb-V微合金钢在1200℃固溶0.5 h后淬火,在650℃回火4 h,利用SEM和HRTEM观察显微组织,合金碳化物的形貌特征和精细结构,用三维原子探针(3DAP)研究合金碳化物中元素分布规律.结果表明,淬火微合金钢在650℃回火4 h后,马氏体板条内位错和板条界面因回复而消失,粗化的合金碳化物分布在原马氏体板条界面和板条内部.同时,伴随着合金元素的再分配,早期析出的圆盘状碳化物沿厚度方向生长,出现一个与基体(M_(bcc))和原碳化物(P_(inner))成半共格关系的新生过渡相(P_(outer)).非碳化物形成元素Si和Al主要分布在碳化物/基体界面处;V和Mn主要分布在碳化物内层,而Mo和Nb分布在整个碳化物区域.粗化的碳化物是一种具有核心和外壳结构的合金碳化物,内层主要是V-Mn-Mo-Nb的碳化物,而外层主要是Mo-Nb的碳化物.     

回火马氏体中合金碳化物的3D原子探针表征Ⅱ.长大

Nb-V微合金钢在1200℃同溶0.5 h后淬火,存450-650℃回火不同时间,用显微硬度和TEM测试并观察析出强化和组织软化现象,用三维原了探针(3DAP)对产生二次硬化的合金碳化物的成分进行定量分析,研究其析出长大规律.结果显示,二次硬化主要是合金碳化物析出强化的作用.随着同火温度的升高或回火时间的延长,合金碳化物的成分动态变化,即强碳化物形成元素取代或部分取代较弱的碳化物形成元素.首先,V和Nb取代Mo,然后Nb部分取代V,最后形成具有一定原子比的合金碳化物.相对回火温度,回火时间对碳化物内合金元素的相对含量影响不大.在合金碳化物长大过程中,薄片状碳化物优先沿径向方向生长,然后沿厚度方向长大并开始粗化.     

合金元素对铁基激光熔覆涂层显微组织和相结构形态的影响

利用CO2激光在45钢表面熔覆制备铁基合金涂层,研究4种合金元素对改变涂层组织形态以及枝晶间碳化物形状的影响规律.结果表明,随着V,Nb,Ti元素和稀土氧化物CeO的依次加入,熔覆涂层原柱状晶形态逐渐改变为柱状树枝晶,最后转变为无明显柱状晶方向性的树枝晶;在激光熔覆涂层中,同时添加V,Nb元素,涂层枝晶间的连续长条状碳化物被打断成块状;同时添加V,Nb,Ti元素和稀土氧化物CeO,涂层枝晶间的碳化物被球化.通过改善涂层树枝晶组织形态以及球化枝晶间碳化物,涂层的抗拉强度和断后伸长率明显提高,涂层的强韧性显著增加.     

铌和钒在高碳钢质焊缝金属中的行为

利用能谱(EDS)及电子探针(EPMA)、透射电镜(TEM)分析了高碳钢质焊缝金属中铌和钒及其碳化物的行为特点，结果表明，Nb可以强烈地改变C的分布和存在状态，导致C在基体固溶体中的显著贫化和高密度NbC质点的析出。改变Nb／C比，可使弥散的碳化物分布在板条马氏体、索氏体、铁素体等不同的基体组织上，与此同时，与Nb共存的Cr失去形成碳化物的倾向，成为固溶强化元素。V有与Nb类似的作用，但其碳化物易沿晶界析出。     

Application of titanium machining chips in welding consumables for wear-resistant hardfacing

Equipment of sugar cane plants and mineral extraction are submitted to severe abrasive wear conditions. Welded hardfacings are usually applied to repair this kind of damage, where commercial chromium/carbon-rich welding consumables have usually been employed. In the present work we investigated the microstructure of experimental hardfacings made by addition of residues (chips) collected from the machining of ASTM F67 (unalloyed Ti, grade 4) alloy. Mixtures with different carbide-formers (Cr/Nb ferro-alloys) were also tested. Two layers of ‘pure’ chips (Ti), chips plus Fe–Cr (Ti–Cr), and chips plus Fe–Nb (Ti–Nb) were applied on low-carbon steel specimens by the GTAW/TIG process. The microstructure of hardfacing layers was observed by optical and scanning electron microscopy (SEM) equipped with EDS microanalysis. The microstructural characterization has determined that carbide distributions change significantly with the chemical nature of the hardfacing. SEM observations coupled with EDS microanalysis have confirmed the formation of complex carbides within the metal weld, whose stoichiometry was determined by X-ray diffraction (XRD) analysis. Mixed carbides of MC type and some cementite have been found. As a result it was suggested that use of ASTM F67 chips as carbide formers for composition of welding consumables can contribute to improved wear resistance of hardfacings, if compared with traditional chromium-based hardfacings.     

合金元素过渡及对堆焊金属硬度的影响

为明确不同合金元素在堆焊金属中的作用,设计了12种碱性药皮堆焊焊条,利用光电直读光谱仪、洛氏硬度计对堆焊金属的成分及硬度进行了测试,分析了C、Ti、Nb、V的合金过渡特点及其对堆焊金属硬度的影响规律.结果表明:C元素过渡波动较大,Nb、V过渡较稳定,各种元素的过渡相互影响;C、V固溶强化作用大,能够提高堆焊金属硬度,而Ti、Nb主要形成碳化物,含量过多时会减弱碳的固溶强化作用,使硬度降低.     

马氏体不锈钢堆焊层组织和耐冲蚀性能

采用2Cr13和经过V、Ti、Nb、N微合金化改性处理的1Cr13马氏体不锈钢进行埋弧堆焊试验,分析微合金元素和热处理工艺对马氏体不锈钢堆焊层显微组织和耐冲蚀性能的影响。研究结果表明:微合金元素V、Ti、Nb与C、N在奥氏体形核初期形成大量颗粒细小、弥散分布的稳定化合物,使堆焊层金属的晶粒得到细化;奥氏体晶粒稳定后,这些化合物又起到析出强化的作用;回火后,部分碳化合物在马氏体板条间析出,起到了二次强化的作用,同时降低马氏体中的碳含量,改善基体韧性。较好的基体强韧性配合最终提高了材料的耐冲蚀性。     

Einflüsse von Mo,V, Nb,Ti, Zr und deren Karbiden auf die Korrosion und Wasserstoffaufnahme des Eisens in Schwefelsäure

Effects of Mo, V, Nb, Ti, Zr and their carbides on the corrosion and hydrogen uptake of iron in sulphuric acid The effects of Mo, V, Nb, Ti, Zr and their carbides on the corrosion and hydrogen uptake of iron in 1 M H₂SO₄/N₂/25°C were investigated by electrochemical and surface analytical methods using binary and ternary Fe-Me alloys with about 0.2 at.-%Me. Due to the experimental conditions, no protective surface layers formed. The transition metals were enriched at the iron surface only as a carbide or oxicarbide. Mo or Zr were not markedly enriched. The corrosion current density and the hydrogen activity were decreased only by Mo or Zr. Hydrogen permeation measurements were analysed in terms of the trapping theory. The average binding energy of shallow traps for hydrogen increases with increasing atomic radius of the substituted alloying elements in the order V, Mo, Ti, Nb and Zr. Correspondingly, the hydrogen diffusion coefficient (after saturation of the deep traps) decreases and the hydrogen solubility increases. The steadystate hydrogen permeation rate remains almost unaffected. The total hydrogen content is determined by the density of deep traps and thus mostly independent of the external hydrogen activity. The trapping effect of iron is strongly increased by dissolved Zr or Nb or in the presence of fine dispersed carbides as VC_x. The effect of coarse carbide particles at a lower density is small.     

多步热处理对GH4742合金组织性能的影响

采用多步热处理,研究了不同固溶温度和高温时效温度对GH4742高温合金组织性能的影响。结果表明,固溶温度显著改变晶粒尺寸和一次γ′相形态。固溶温度为1090 ℃时,基体中存在大量未溶的一次γ′相,可以有效阻止晶粒长大,同时这种粗大γ′相以及后续时效过程中形成的细小γ′相共存的组织使得合金具有良好的综合力学性能。高温时效处理对组织形貌影响较小,但可以改变γ′相的尺寸,显著影响晶界碳化物的形态,通过Mo置换一次碳化物MC中的Nb、Ti,使晶界连续分布的碳化物发生溶解形成颗粒状的碳化物,显著降低了GH4742高温合金的高温持久性能。     

热等静压冷速对SLM成形K536合金力学性能的影响

采用激光选区熔化工艺制备K536航空发动机零件,研究了不同冷速的热等静压HIP工艺对制件组织及力学性能的影响。结果表明,激光选区熔化K536高温合金制件经HIP处理后,制件内部产生完全再结晶,金相组织为奥氏体基体及晶内和晶界碳化物,合金强度降低、塑性上升,数据分散性下降;随HIP冷速的增大,组织中晶界碳化物减少,晶内出现少量颗粒状碳化物,有效提升了合金在815℃的高温屈服强度。     

The influence of welding condition on the microstructure of WC hardfacing coating on carbon steel substrate

Tungsten carbide (WC) hardfacing coating technique is widely used to improve the performance of carbon steel blade exposed to acidic and abrasive conditions during production. This paper deals with the influence of welding parameters on the microstructure and carbide distribution of WC. WC hardfacing was deposited onto carbon steel by shielded metal arc welding (SMAW). Welding parameters such as welding current, number of weld layers, electrode drying and base material preheat were the focus of this work. Coating hardness, microstructure and elemental composition were analysed in detail. The effects of the welding parameters on WC hardfacing coating microstructure and hardness value were characterized by scanning electron microscope (SEM) and micro-Vickers hardness tester respectively. The larger carbide growth in overall coating region is mainly dictated by high current (200 A), increased number of weld layers (3 layers) and presence of base material preheat due to sufficient heat energy initiating carbide growth. The investigation also revealed that high current affected the growth of smaller carbide particles in matrix region significantly. Meanwhile, number of weld layers and base material preheat influences were seen during hardfacing with lower welding current. The absence of electrode drying led to uniform smaller carbide distribution in matrix region. It was found that increased number of large carbides and uniformly distributed smaller carbides in WC hardfacing deposit increased the hardness value of the coating.     

Relationship between phase composition and corrosion resistanceof Ni-Ti-Nb based shape memory alloys

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粉末冶金碳化物强化铌合金组织演变及其力学行为

采用机械球磨与热压烧结相结合的粉末冶金法对不同球磨时间Nb-35Ti-6Al-5Cr-8V-5C合金的粉末变形行为,微观组织结构和力学行为进行研究。结果表明:随着球磨时间的增加,Nb-35Ti-6Al-5Cr-8V-5C复合粉末中的块状金属颗粒首先变形为片状后在碰撞挤压作用下破碎成絮状,TiC粉末均匀的分布于片状金属粉末表面;Nb-35Ti-6Al-5Cr-8V-5C合金由Nbss和(Nb,Ti)C两相构成,各合金碳化物体积分数均为11%左右,Ti元素主要分布于Nbss晶界和碳化物内,Al、Cr、V元素主要分布于Nbss晶粒内,Nbss和(Nb,Ti)C相尺寸均随球磨时间增加而尺寸减小;Nbss晶粒细化及强化相碳化物弥散化导致合金的室温压缩力学性能和塑性变形能力显著提高,压缩变形后合金Nbss与碳化物具有良好的界面结合能力,但是碳化物内部存在明显的近似平行分布的裂纹;数据对比表明,粉末冶金法制备Nb-35Ti-6Al-5Cr-8V-5C合金的力学性能优于电弧熔炼法。     

碳化物对铌基多相合金力学性能和组织结构的影响

采用纳米压痕和原子力显微镜对Nb-21Ti-4C-x Al(x:0,5,10,15 at%,下同)、Nb-35Ti-4C及Nb-25Ti-8C合金Nbss、(Nb,Ti)C、Nb3Al及相界面的力学性能和变形行为进行了研究。研究表明:Ti、Al元素合金化能有效提高Nbss的硬度,且Al强化效果优于Ti;高硬度的碳化物、Nb3Al与Nbss界面结合良好是理想的增强相。热处理后(Nb,Ti)C内部析出二次Nbss,改善了碳化物的变形行为,提高了韧性;热处理后Nbss内部组织均匀化及位错密度降低导致Nbss硬度下降。Ti、Al、C原子含量变化及热处理对Nbss的弹性模量影响不大。