中频熔敷WC、铬铁、SiC增强铁基复合层组织和耐磨性研究

为了进一步提高Fe55自熔性舍金粉末熔敷层的耐磨性能,在Fe55合金粉末中添加了碳化钨、铬铁、碳化硅颗粒,利用中频感应加热在42CrMo钢表面进行熔敷.通过正交试验研究了碳化钨、铬铁、碳化硅颗粒加入量对熔敷层组织、结构、硬度及耐磨性的影响.研究表明:铬铁添加量在10％,碳化钨添加量在8％,碳化硅添加量在3％时,熔敷层组...     

B,RE,La对锶变质A356铝合金微观组织及力学性能影响

对比研究了B,RE,La对锶变质A356铝合金微观组织与力学性能的影响。结果表明,钛、硼联合细化,晶粒细化效果最明显。经0.01%Ti、0.03%B联合细化的0.04%Sr变质的A356铝合金晶粒细小,硅颗粒细碎、圆整,具有最好的力学性能。     

Atom probe tomography and nano secondary ion mass spectroscopy investigation of the segregation of boron at austenite grain boundaries in 0.5 wt.% carbon steels

The grain boundary segregation of boron atoms in high strength low alloy steels containing 50 ppm boron was accomplished using atom probe tomography (APT) and nano-beam secondary ion mass spectroscopy (SIMS). The formation of boro-carbides under an excessive addition of boron to the steels was identified through the SIMS and TEM. The APT was performed in order to evaluate the composition of the alloying elements, such as, boron and carbon, segregated at prior austenite grain boundaries. The boron contents at the prior austenite grain boundaries were approximately 1.7 ± 0.2 at.%, which was approximately 70 times more than the amount of boron added to the steels.     

碳和硼对高铼含量的定向凝固镍基高温合金元素偏析行为的影响

研究元素碳和硼对含铼镍基定向柱晶高温合金相转变温度、元素偏析和碳化物析出相的影响。结果表明：随着碳含量的增加,液相线温度逐步降低,而碳化物的析出温度上升。硼的添加造成合金液相线温度、碳化物析出温度和固相线温度均下降。随着碳含量的增加,铼元素的偏析先增大后减小,而其它元素的偏析程度变化并不是很大。铼、钨、钽的偏析随硼的加入而逐渐增大。合金中碳化物的形态主要为汉字体状,碳化物数量随着碳含量的增加逐渐增大。添加硼元素的合金中析出的碳化物较不含硼元素的合金中析出的碳化物更加集中和粗大。     

碳化铌对铁基碳化钨耐磨堆焊合金中碳化钨溶解的影响

采用自行研制的铁基碳化钨耐磨堆焊药芯焊丝,通过钨极氩弧焊(TIG)在Q235上制备Fe-Nb-C-B-Ni-WC(30%)合金.改变合金中铌含量(1.0%,2.5%,3.8%),研究铌含量对Fe-Nb-C-B-Ni-WC(30%)合金中碳化钨溶解的影响.结果表明,铌含量对合金中碳化钨的溶解程度有很大影响,优先在碳化钨周围生成的细小NbC对碳化钨溶解起抑制作用,而其生成量决定了抑制碳化钨溶解作用的强弱.铌含量为2.5%的合金中生成的NbC有效的抑制了碳化钨的溶解,使碳化钨颗粒保留的比较完整.     

淬火温度对Fe-Cr-B-C合金涂层组织及硬度的影响

利用等离子堆焊工艺制备了Fe-Cr-B-C合金涂层,并对其进行了不同温度(850、950和1050 ℃)的淬火处理。利用OM、SEM、XRD研究了合金涂层不同温度淬火后的显微组织,利用显微硬度计对合金涂层的硬度进行了测试。结果表明:堆焊态Fe-Cr-B-C合金涂层的显微组织由树枝晶基体和网状硼碳化物组成;经1050 ℃淬火处理的Fe-Cr-B-C合金涂层网状硼碳化物回溶、球化,硬度达64.3 HRC,综合性能最优。     

Effect of size and distribution of titanium carbide on microstructure and mechanical properties of Ti-25V-15Cr-2Al-0.2C-0.2Si alloy

The effect of size and distribution of titanium carbide on the microstructure and mechanical properties of non-burning β titanium alloy Ti-25V-15Cr-2Al-0.2C-0. 2Si （mass fraction, %） was investigated. The microstructure of the heat-treated and exposed alloy was studied using optical microscopy（OM）, scanning electron microscopy （SEM） and transmission electron microscopy（TEM）. It is found that carbides with finer size and more uniform distribution can suppress the formation of α precipitates more effectively, and can especially decrease the amount of grain boundary α precipitates after long-term exposure at 540 ℃ （the expected application temperature）. Thus, significant improvement in thermal stability can be achieved by refining carbide particles in the matrix of the alloy.     

氩气保护下碳化钨对镍基合金熔覆层组织及耐磨性的影响

目的改善Q235钢板的耐磨性,以取代65Mn在振动筛筛板中的应用。方法采用电阻丝加热非真空熔覆技术,在氩气保护条件下于Q235钢表面制备碳化钨/镍基合金复合熔覆层。通过SEM和XRD观察分析熔覆层与基体的结合方式、碳化钨分布、熔覆层组织及相组成,通过硬度测试及磨损试验,分析碳化钨对熔覆层耐磨性的影响。结果熔覆层与钢基体达到冶金结合。熔覆层主要由奥氏体、碳化钨、碳化物及硼碳复合化合物等相组成,碳化钨弥散分布其中。当碳化钨用量为熔覆粉末总质量的35%时,熔覆层硬度为47.3HRC,磨损率为0.08 mg/m,约是钢基体耐磨性的5倍,65Mn耐磨性的4倍。结论采用氩气保护制备的碳化钨熔覆层与基体结合良好,提高了钢基体的耐磨性。     

SPS制备致密碳化硼陶瓷的结构及性能

以富硼碳化硼粉体为原料,采用放电等离子烧结(SPS)制备致密碳化硼陶瓷体,研究了SPS工艺对碳化硼陶瓷结构和性能的影响.结果表明,SPS烧结工艺可以低温快速烧结得到致密度达到99.7%的碳化硼陶瓷体,烧结温度和烧结时间对碳化硼的致密度和晶粒尺寸都有影响.烧结过程中样品晶粒表面产生玻璃相,玻璃相的存在使碳化硼断裂机制由穿晶断裂过渡为沿晶断裂,有助于提高材料断裂强度和断裂韧性.SPS制备的致密碳化硅陶瓷材料具有良好的力学性能,其中致密度达到99.6%,抗弯强度达到550.1 MPa,硬度39.52 GPa.     

中粗WC含量对Ni-Co粗晶硬质合金微观组织及性能的影响

研究了中粗WC含量对Ni-Co粗晶硬质合金微观组织与晶粒分布的影响,进而讨论了晶粒分布对硬质合金力学性能的影响。通过金相分析了中粗WC含量对硬质合金晶粒度与邻接度的影响,并利用截线法研究了微观组织的晶粒的分布规律;研究了晶粒度与晶粒分布对磁力、密度及其它力学性能的影响。结果显示,中粗WC晶粒可均匀分布在粗晶WC周围阻碍粗晶与粘结相接触,抑制了粗晶粒的快速粗化,降低了合金平均晶粒度与平均自由程,使晶粒分布逐渐转变为双峰分布;在压力烧结下所有合金的相对密度均在99.5%以上,通过对矫顽磁力的测试分析,验证了微观组织中晶粒双峰分布的准确性;平均晶粒度的降低使合金硬度逐渐增加、断裂韧性逐渐降低;微观组织中超粗晶粒逐渐减少,有利于硬质合金抗弯强度与耐磨性的提高。在Ni-Co粗晶硬质合金中加入部分中粗WC颗粒有利于减少晶粒粗化进而提高耐磨性,加入30%中粗WC颗粒时综合性能最好。     

Microstructure of vacuum plasma-sprayed boron carbide

In the present study, boron carbide was deposited on Ti-6%Al-4%V alloy by vacuum plasma spraying. Chemical and phase compositions of the initial starting powder and the as-sprayed deposit were characterized using hot gas extraction, x-ray photoelectron spectroscopy, Raman spectroscopy, x-ray diffraction, and transmission electron microscopy. Mechanical properties of the deposition were assessed by microhardness and nanohardness indentation. The microstructure consisted of equiaxed boron carbide grains, microcrystalline particles, and amorphous carbon regions. The amount of boron oxide and amorphous carbon in the coating was increased compared with the initial powder. The measured microhardness was slightly higher than values reported previously (1033±200 HV). There was significant variation in measured nanohardness (−100 + 39 GPa) from point to point caused by multiple phases, splat boundaries, and porosity in the deposited structure. Carbon segregation to grain boundaries and/or splat boundaries in boron carbide was observed directly using spatially resolved electron energy loss spectroscopy method.     

Investigation on mechanical properties of aluminium 7075-boron carbide-coconut shell fly ash reinforced hybrid metal matrix composites

The present research work reports the fabrication and evaluation of the mechanical properties of hybrid aluminium matrix composites(HAMC). Aluminium 7075(Al7075) alloy was reinforced with particles of boron carbide(B_4 C) and coconut shell fly ash(CSFA). Al7075 matrix composites were fabricated by stir casting method. The samples of Al7075 HAMC were fabricated with different weight percentages of(0, 3, 6, 9 and 12 wt.%) B_4 C and 3 wt.% of CSFA. The mechanical properties discussed in this work are hardness, tensile strength, and impact strength. Hardness of the composites increased 33% by reinforcements of 12 wt.% B_4 C and 3 wt.% CSFA in aluminium 7075 alloy. The tensile strength of the composites increased 66% by the addition of 9 wt.% B_4 C and 3 wt.% CSFA in aluminium 7075 alloy. Further addition of reinforcements decreased the tensile strength of the composites. Elongation of the composites decreased while increasing B_4 C and CSFA reinforcements in the matrix. The impact energy of the composites increased up to 2.3 J with 9 wt.% B_4 C and 3 wt.% CSFA addition in aluminium alloy. Further addition of reinforcement decreased the impact strength of the composites. The optical micrographs disclosed the homogeneous distribution of reinforcement particles(B_4 C and CSFA) in Al7075 matrix. The homogeneously distributed B_4 C and CSFA particles added as reinforcement in the Al7075 alloy contributed to the improvement of hardness, tensile strength, and impact strength of the composites.     

B元素对Fe-Cr-C系耐磨堆焊合金组织和耐磨性的影响

采用直径为1.6 mm的细径药芯焊丝,利用CO₂气体保护焊堆焊的方法制备了含有1.0%~3.0%C(质量分数),15%~20%Cr,0%~2.0%B的高铬堆焊合金.研究了B₄C含量对堆焊合金的硬度及耐磨性的影响.结果表明,堆焊合金的硬度从57.1 HRC增加到65.2 HRC,硬度提高14.2%;堆焊层合金的相对耐磨性从3.5倍提高到18.0倍.借助光学显微镜、扫描电镜和X射线衍射等微观分析方法,研究了堆焊合金的显微组织及碳化物分布形貌.结果表明,堆焊合金的显微组织主要由铁素体+奥氏体+(Fe,Cr)₇C₃组成,加入B₄C可显著改善堆焊合金层基体组织,使碳化物(Fe,Cr)₇C₃数量增加且呈弥散分布.     

C含量对单晶高温合金再结晶的影响

采用选晶法在真空定向凝固炉中,制备了C含量分别为0.019%、0.048%、0.074%和0.094%的单晶高温合金,合金表面吹沙后分别在1 250、1 300℃进行真空热处理,研究不同C含量对单晶高温合金再结晶的影响。结果表明:随着合金中C含量升高,碳化物含量增多,其形态由块状转变为骨架状、发达骨架状;随着C含量增加,合金再结晶层深度无明显变化趋势,这表明碳化物对合金再结晶无明显的抑制作用,随着热处理温度升高,再结晶厚层深度明显增加;C对单晶高温合金再结晶抑制作用与形成碳化物的形态和密度有关,在合金表层形成高密度的碳化物,从而对再结晶晶界形成钉扎作用,阻碍晶界的迁移,能够起到抑制再结晶的作用。     

Effect of tungsten carbide nanoparticles on mechanical properties and sinterability of B4C-WC nanocomposites using pressureless sintering method

The effect of tungsten carbide (WC) nanoparticles on sinterability and mechanical properties of boron carbide is investigated in this study. Boron carbide, being one of the hardest materials nowadays, has a variety of applications in wear-resistant components such as cutting tools. The low strength and low fracture toughness property of this material is the drawback in its application. Production of high density boron carbide is a problem due to its covalent bonds, low plasticity, surface energy and self-diffusion ratio, high resistance to slide in the grain boundaries etc… Boron carbide samples containing 5,10,20 and 30 vol.% WC were manufactured by firstly cold press and then sintering at three elevated temperatures of 2150 °C, 2200 °C and 2250 °C. It observed that addition of WC nanoparticles results in increase in mechanical properties and density of boron carbide. The highest increase is in the 30 vol.% sample with sintering temperature of 2250 °C were the density is improved by 23%, hardness by 33%, Young's modulus by 53%, and fracture toughness by 38% compared to pure boron carbide.     

Investigation on addition of talc on sintering behavior and mechanical properties of B4C

The effect of high alumina talc powder as a sintering aid on densification of boron carbide powder was investigated. The in situ reaction of talc with boron carbide generate SiC, MgB₂, and alumina, which all aid the sintering process and permit pressureless sintering at temperatures between 2050 and 2150°C. The microstructure-property relationship has been studied in the B₄C-talc system for talc content between 0 and 30 wt.%. It became clear the addition of talc powder has a significant effect on the sintering behavior of B₄C. B₄C composites along with talc powder additions were sintered up to 98% of theoretical density. The mechanical properties were improved over those of samples without talc addition.     

Effect of minor Sc and Zr addition on grain refinement of as-cast AI-Zn-Mg-Cu alloys

The optical microscopy and scanning electron microscopy as well as energy dispersive spectroscopy were employed to investigate the influence of joint addition of Sc and Zr on grain refinement of AI-Zn-Mg-Cu alloys.Results show that the addition of 0.20% Sc has a little effect on grain refinement because Sc is mainly dissolved into the matrix and hardly any primary Al3Sc particles are precipitated. The alloy with addition of 0.30% Sc and 0.16%Zr has more equiaxed grains than that of others,giving cast grain sizes as fine as 13μm. This is because the Sc substitutes for AI atom in the AI-Zr crystal cell and forms AI-Sc-Zr unit cell,which grows and becomes AI3(Scx,Zr1.x)particle,acting as a nucleus for the formation of a-AI. The addition of 0.04% Ti and 0.008% B makes the grain size drop from 250 μm to 50 μm. Its refinement effect is less than the 13 μm achieved by the alloy including 0.30% Sc and 0.16% Zr.     

EFFECT OF NITROGEN ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ALLOY HK50

The volume fraction of the lamellar carbide cell in HK50 alloy may be increased with the in-crease of nitrogen content over 0.065%.The habit plane of lmellar carbide is {111}_γ.Thedistribution of nitrogen changes no more before or after the precipitation of lamellar structure.The diffusion activation energy of carbon reduces remarkably with the increase of nitrogencontent.It is believed that the lamellar carbide cell is harmful to the high temperature creepand impact properties of the alloy.     

碳化硼对高熵合金结构及性能的影响

采用微波烧结工艺制备B₄C/FeCoNiCrAl与B₄C/FeCoNiCrCu高熵合金基复合材料,研究了不同含量的B₄C对FeCoNiCrAl、FeCoNiCrCu高熵合金组织结构和性能的影响。结果表明:B₄C的添加一定程度上增加了基体合金的晶格畸变,合金微观组织由高熵合金基底区、碳化硼分解生成的硼化物区和碳化物区3部分构成。体心立方结构的FeCoNiCrAl高熵合金中硼化物为针状,面心立方结构FeCoNiCrCu高熵合金中硼化物组织为块状,这与合金体系中的原子尺寸差相关。B₄C可显著提高合金的强度和硬度,塑性略有下降。4%B₄C/FeCoNiCrAl合金复合材料具有最高的硬度和压缩强度值,分别为627.1 HV0.5和1836 MPa,但是塑性较差,压缩比仅为11%;而4%B₄C/FeCoNiCrCu合金复合材料硬度与强度仅为249.3 HV0.5与1413 MPa,低于4%B₄C/FeCoNiCrAl复合材料,但塑性较好,压缩比可达35%。     

Martensitic transformation of Ti-18Nb(at.%) alloy with zirconium

The addition of 3%～9% Zr on the martensitic transformation of Ti-18Nb(at.%) alloy was investigated. The results of microstructure and X-ray diffraction (XRD) analysis show that the phase constitution of as-quenched Ti-18Nb-9Zr(at.%) alloy consists of the retained matrix and martensite, while that of the other three alloys is single martensite. No trace of athermal phase was found in any of the as-quenched alloys. Unlike the effect of Nb addition on the martensitic transformation start temperature Ms of Ti-1...