Si影响M2高速钢中共晶碳化物的精细研究

通过金相、扫描电镜、X射线衍射、能谱分析等方法对添加不同Si量的M2高速钢中的共晶碳化物进行了精细研究。结果表明,添加1%Si后,M2高速钢铸态组织中共晶碳化物的类型和形貌都没有明显变化,仍以层片状M2C碳化物为主;添加2%和3%Si后,铸态组织中的共晶碳化物变为"鱼骨"状M6C碳化物,层片状M2C共晶碳化物已完全消失;此外,随着含Si量的增加,高速钢铸态组织枝晶间距减小。     

M2铸造高速钢的变质处理

用Re Al N复合变质剂对M 2铸造高速钢进行变质处理 ,消除了钢中网状共晶碳化物 ,细化了基体组织 ,减轻了W、Mo元素偏析 ,在不降低M 2高速钢硬度的情况下 ,韧性大幅度提高 ,经 1180～ 12 0 0℃淬火 ,5 6 0℃三次回火后 ,硬度保持在HRC6 5～ 6 6 ,冲击韧性由 8.5J提高到 17.0J。变质处理M 2铸造高速钢具有优异的抗热疲劳性能和抗高温磨损性能     

三维原子探针表征淬回火Cr-Mo-V-Ni中合金钢的元素分布

将Cr-Mo-V-Ni中合金钢在1 030℃奥氏体化保温0.5h后油淬,在600℃回火2次,每次2h。结合光学显微镜(OM)和扫描电子显微镜(SEM),采用三维原子探针(3DAP)技术分析了淬火态和回火态各元素原子的三维空间分布以及碳化物内部和碳化物/基体界面处元素分布和成分变化。结果表明,淬火试样中C原子由于自回火和短程扩散出现了较为明显的片状偏聚,而其他合金原子Cr、Mn、Mo、Si、V和Ni基本分布均匀;回火试样中C、Cr、Mo和V发生共偏聚形成厚度约10nm的合金碳化物M23C6,Si原子形成一层薄薄的偏聚层包裹着M23C6,而Ni又包裹着Si原子而偏聚于最外层。     

硅对烧结M3∶2高速钢回火相及力学性能的影响

为研究硅对烧结高速钢力学性能的影响,采用真空热处理炉在1230℃对含0.4%碳粉及硅添加量在0～3.0%的M3∶2高速钢进行烧结,在500～600℃对烧结后的试样进行二次回火.采用X射线衍射仪,扫描电镜及能谱分析等手段研究了不同硅添加量对回火态高速钢的物相特征及力学性能的影响规律.物相分析结果表明,添加硅后,硅主要分布在回火马氏体及M6C碳化物中,而在MC碳化物中含量较低.回火马氏体组织中硅的含量随硅添加量的增加而增加,同时,硅的添加还显著影响回火马氏体组织中铁素体相的晶格常数,在硅添加量为0.7%时,铁素体相达到最大的晶格常数.力学性能测试结果表明,适量硅的添加可提高二次硬化效果,添加0.7%硅的高速钢在550℃二次回火后获得了最佳的硬度和弯曲强度.     

轧辊用高速钢中碳化物研究

本文利用扫描电镜、能谱分析对三种轧辊用高速钢的组织中碳化物进行了研究,并分析了VC形态与高速钢化学成分之间的关系。结果表明：轧辊用高速钢组织包括马氏体基体,残余奥氏体和各种类型碳化物,如粒状或小块状的MC型碳化物,网状的M7G型碳化物,鱼骨状的M6C型碳化物以及其他复合型碳化物,各种碳化物含有的合金元素以及显微硬度不同;在研究范围内（Weq≤10）,晶粒尺寸是随钨当量的升高而变小;根据V含量不同,VC会出现不同形貌进而影响高速钢性能。     

一种多元低合金高碳钢的热处理组织及硬度的研究

对一种低合金高碳钢(0.81C,0.65Cr,0.89W,0.54Mo,0.23V)热处理组织及硬度研究表明,该钢退火具有多类型碳化物(M3C,M7C3,M23C6,M6C和MC),在800～840℃区间退火,处于γ相低温区原碳化物部分溶解和新碳化物重新形核生长过程,使碳化物颗粒超细化,平均尺寸0.33～0.34 μm.淬火时,因M3C、M23C6溶解于奥氏体的速度较快,在840～860℃淬火时,硬度可达HRC63～65;未溶碳化物M6C和MC(VC)有利于马氏体细化,但因其数量较少,淬火最高温度不易超过880℃.该钢在低温和中温回火有较好的抗回火性能,并能有效地促进残余奥氏体转变.该钢热处理过程组织结构特征能较好地以相平衡热力学计算结果进行解释.     

轧辊用高速钢组织与性能研究

研究了四种不同成分的轧辊用高速钢淬火和回火后的显微组织与性能。结果表明,轧辊用高速钢合适的淬火温度为1050℃～1100℃,回火温度为500℃～550℃,热处理后组织由回火马氏体、少量残余奥氏体以及各种碳化物组成,大量细小碳化物呈弥撒分布,铸态组织中网状碳化物基本消除。回火后高速钢硬度可达HRC62,冲击韧性在6J／cm^2以上,可以满足制作高速钢轧辊的要求。     

利用JMatPro软件进行合金覆层成分设计及回火工艺制定

利用JMatPro软件对合金覆层进行计算,模拟分析了不同回火状态下合金覆层内部相组成成分的变化情况与碳化物颗粒的析出情况,预测了合金覆层的相关性能;采用微束等离子熔覆加工方法,在H13钢基体上熔覆制备了合金覆层,研究分析了合金覆层回火前后的组织形态、物相组成、元素分布和显微硬度变化。结果表明,对合金覆层进行200℃回火2 h,合金覆层内部组织结构、物相组成与回火前相比无明显变化,显微硬度也无明显变化(463 Hv_0.1);经400℃回火2 h后,合金覆层组织内部开始有少量MC型特殊碳化物析出,晶界周围逐渐呈现不连续的网状分布,一定程度上提升了覆层的显微硬度(512 Hv_0.1);经600℃回火2 h后,合金覆层组织内部析出大量MC、M2C型特殊碳化物,之前不连续的网状分布发展为连续、密集的蛛网状分布,合金覆层内部整体呈现出更为细小、均匀的组织形态,覆层硬度提升约25.88%,达到569 Hv_0.1。     

激光表面重熔对高速钢显微组织的影响

采用CO_2连续波激光对W18Cr4V高速钢进行表面重熔处理。分析结果表明,经激光重熔后高速钢的显微组织明显细化,重熔层内的相构成为马氏体、奥氏体,过剩的δ铁素体和M_6C、M_(23)C_6型碳化物。枝晶内为孪晶马氏体和部分板条马氏体。枝晶间为富合金元素的奥氏体和M_6C碳化物,孪晶马氏体上沿孪晶面有M_(23)C_6碳化物共格析出。激光扫描速度增加、δ铁素体量增多,重熔层显微硬度下降。     

高速钢激光相变强化组织的回火稳定性

研究了Ｗ１８Ｃｒ４Ｖ高速钢激光相变强化层的组织及其回火稳定性。结果表明,对于Ｗ１８Ｃｒ４Ｖ高速钢,激光相变强化后的组织明显细化,其组织由马氏体,残余奥氏体及末溶碳化物组成,Ｗ,Ｃｒ,Ｖ等强碳化物形成元素在马氏体及残余奥氏体中固溶度的提高使强化层的回火稳定性有了明显的改善,经６４０℃回火后强化层硬度达到最高值１００３ＨＶ０．１,红硬性的提高改善了高速钢刀具的切削性能。     

球磨工艺对炭气凝胶(CA)-SiO复合材料结构和电化学性能的影响

单纯的炭气凝胶(CA)与SiO球磨后可以制得性能优异的复合材料CA-SiO, 实验研究了球磨时间和球磨转速等工艺条件对CA-SiO的结构和电化学性能的影响. 结果表明, 无定形态的SiO与CA球磨后, 逐渐有晶粒细小的Si晶体析出, Si的晶粒随球磨时间的延长或球磨转速的提高先减小然后增大, Si的结晶度随球磨时间的延长或球磨转速的提高而增强, 但过长的球磨时间或过快的球磨转速均会导致材料中的晶体Si向非晶态转变; 球磨使材料中C的晶粒有所增大, 但球磨时间和球磨转速对C的晶粒大小没有明显的影响; CA-SiO中Si的结晶度越高、晶粒越小, 材料的嵌脱锂容量越高、充放电循环稳定性越好, 非晶态Si的存在不仅不利于锂离子在CA-SiO中的嵌入和脱出, 而且会导致材料的循环稳定性变差. 将CA-SiO用作锂离子电池负极材料时, 其最佳的制备工艺为: 以400r/min的速度球磨10h.     

硅基沉积氮化镓,碳化硅,III –V 族及其合金材料研究进展

硅基沉积氮化镓, 碳化硅, III-V 族及其合金材料是近年来的研究热点. 氮化镓, 碳化硅及其III-V 材料在光电子和电子元件领域有着广泛的应用.例如大功率, 高速器件, 大型激光器, 紫外探测器等等. 尽管硅基片具有低成本, 大的尺寸,和极好的电热导性能等优点, 硅基片仍没有成为氮化镓, 碳化硅及III – V 的主要沉积基片, 其原因在于硅基片与氮化镓, 碳化硅及III-V 材料之间的热膨胀系数和晶格常数之间的失配. 自从1998年, IBM 的课题组用分子外延方法在硅基片上沉积氮化镓, 并且成功地制备了氮化镓激光器之后, 硅基氮化镓的研究开始备受关注. 近年来的研究发现, 使用氧化铝和氮化铝镓作为过渡层. 硅基氮化镓的热应力及与硅基片之间的晶格失配可以明显降低.在 6英寸的(111) 取向的硅基片上用化学气相方法可以成功地沉积超过一个微米厚的无裂纹的单晶氮化镓. 德国的AZZURRO 公司成功地制备硅基片氮化镓的大功率的蓝色激光器. 美国的NITRINEX公司也生产了硅基氮化镓大功率电子元件. 超大功率的硅基氮化镓电子元件仍在研究中. 在2007年, 英国政府设立了一个固体照明器件的研究项目. 主要着手研究6英寸的硅基氮化镓激光器. 另一方面, 在过去的40年, 超大规模硅基CMOS 技术已有了长足的发展, 下一代低功耗高速逻辑电路要求低的驱动电流, 小的活门尺寸低于 30 nm 和快速反应性能. 这就要求器件通道材料具有很高的电子(或空穴)迁移率. III-V 材料, 例如InSb, InAs, 和InGaAs 具有电子迁移率高达 80000 cm2/VS. 它们将是下一代低于 30 nm 硅基CMOS 器件最好的候选材料. 在 2007 年美国DARPA/MTO 设立了一个研究项目来发展硅基 III-V材料器件, 着重于发展高速硅基III-V材料CMOS 器件. 第一届”硅基氮化镓,碳化硅,III-V及其合金材料研究进展 ”国际会议也将于3月 24日-28日在旧金山MRS 2008年初春季会议上召开.     

Fabrication of Al–Si coating on Ti–6Al–4V substrate by mechanical alloying

Al–Si coatings were synthesized on Ti–6Al–4V alloy substrate by mechanical alloying with Al–Si powder mixture. The as-prepared coatings had composite structures. The effects of Al–Si ratio, milling duration and rotational speed on the microstructure and oxidation behavior of coating were investigated. The results showed that the continuity and the anti-oxidation properties of the coating were enhanced with the increase of Al–Si weight ratio. The thickness of the coating largely increased in the initial 5-hour milling process and decreased with further milling. A rather long-time ball milling could result in the generation of microdefects in coating, which had an adverse effect on the oxidation resistance of coating. Both the thickness and the roughness of the coating increased with the raise of rotational speed. The low rotational speed would lead to the formation of discontinuous coating. The rotational speed had a limited effect on the coating oxidation behavior. Dense, continuous and high-temperature protective Al–Si coatings could be obtained by mechanical alloying with Al–33.3?wt.%Si powder at the rotational speed ranging from 250 to 350?rpm for 5?h.     

Ultralong zinc-blende ZnS nanowires grown on polar C face of 6H-SiC substrates at low temperatures by metalorganic chemical vapor deposition

Ultralong ZnS nanowires with high purity were grown on Au-coated polar C face of 6H-SiC substrates via metalorganic chemical vapor deposition at low temperatures. The ZnS nanowires have zinc-blende structure and the length is up to tens of micrometers. HRTEM investigations show that the nanowires are well crystalline single crystal grown along [1 1 1] and free of bulk defects. However, sparse straight and curved nanowires with poor crystalline nature are randomly grown on the Au-coated Si face of 6H-SiC substrates. We deduce that the growth of ZnS is related to the substrates and C face can enhance Au-catalytic VLS growth. The CL spectra of an individual nanowire grown on C and Si face reveal different optical properties. Intrinsic sulfur and zinc vacancies are the main reasons for the 458.1 nm and 459.2 nm blue emission detected in the nanowire grown on C face and Si face, respectively. Nevertheless, an unusual green emission at 565.1 nm is observed in the poor crystalline nanowire grown on Si face, which originates from the bulk defects.     

Si(111)衬底上6H-SiC薄膜的低压化学气相外延生长与表征

在Si(111)衬底上,采用SiH4-C3H8-H2气体反应体系,通过低压化学气相沉积(LPCVD)工艺外延出结晶质量良好的SiC薄膜.低温光致发光谱表明该薄膜属于6H-SiC多型体.X射线衍射图表明该薄膜具有高度的择优取向性.扫描电子显微镜图表明该薄膜由片状SiC晶粒组成.拉曼光谱和透射电子衍射谱的结果进一步表明该薄膜具有较高的结晶质量.对Si(111)衬底上6H-SiC薄膜的生长机制进行了初步探讨.     

Effect of growth parameters on the heteroepitaxy of 3C-SiC on 6H-SiC substrate by chemical vapor deposition

Epitaxial 3C-SiC(1 1 1) films were grown on 6H-SiC(0 0 0 1) Si face on axis substrates by chemical vapor deposition under H₂, SiH₄ and C₃H₈ in a cold wall vertical reactor. Two temperatures were studied (1450 and 1700 °C) with various C/Si ratio and deposition time. It was found that under conditions giving high lateral growth (low C/Si and/or high temperature), homoepitaxial growth occurred even at temperatures as low as 1450 °C. For other conditions, the 3C-SiC polytype was detected and always together with the formation of double positioning boundaries whose density was found to depend on the growth conditions but not on the initial surface reconstruction. Single domain enlargement was observed when growth was performed at 1700 °C over a nucleation layer grown at 1450 °C.     

Microstructure and properties of Sip/Al–20 wt% Si composite prepared by hot-pressed sintering technology

In the present work, 50 vol% Sip/Al–20Si composite was prepared by hot-pressed sintering technology. Si particles were uniformly distributed in the Sip/Al–20Si composite, and only the presence of Si and Al phases were detected by XRD analysis. Dislocations, twins, and stacking faults were found in the Si particles. Several Si phases were found to be precipitated between Al matrix and Si particles. Si/Al interface was clean, smooth, and free from interfacial product. HRTEM indicated that the Si/Al interface was well bonded. The average CTE and thermal conductivity (TC) of Sip/Al–20Si composite were 11.7 × 10^?6/°C and 118 W/(m K), respectively. Sip/Al–20Si composite also demonstrated high mechanical properties (bending strength of 386 MPa). Thus, the comprehensive performance (low density and CTE, high TC, and mechanical properties) makes the Sip/Al–20Si composite very attractive for application in electron packaging.     

合成一维β-SiC纳米材料原料粉体的球磨工艺研究

采用高能球磨对合成一维β-SiC纳米材料的原料-Si粉和SiO2粉分别进行处理。通过正交试验研究球磨转速、时间、球料比、级配比等因素对球磨后粉体粒径的影响规律,结果表明,Si粉的球磨优化工艺为转速300r/min、球磨时间4h、球料比5:1,级配比φ20 mm:φ10 mm:φ6mm:φ2mm=1:50:180:400;SiO2粉的球磨优化工艺为转速350 r/min、球磨时间4.4 h、球料比15:1,级配比φ20mm:φ10mm:φ6mm:φ2mm=1:50:180:400。借助粒度分析仪及透射电子显微镜(TEM)对产物进行表征,发现经过球磨处理后的粉体粒度分布均匀,比表面积提高,可用以合成高质量的一维β-SiC纳米材料。     

Oxide and interface characteristics of oxidized silicon oxynitride ceramics – an investigation by electron microscopy

Hot-isostatically pressed silicon oxynitride (Si2N2O) ceramics free from sintering aids were oxidized in 1 atm dry oxygen at 1100 and 1300°C. The structural and chemical characteristics of the oxide and the nature of the oxide–Si2N2O interface were determined using cross-sectional transmission electron microscopy in conjunction with small-probe energy dispersive X-ray analysis and selected-area electron diffraction. Oxidation of Si2N2O resulted in the formation of amorphous SiO2. The oxide–Si2N2O interface was chemically abrupt. The interface was very flat when parallel to low-index, high atomic density Si2N2O crystal planes but became notably undulated if oriented to high index, low atomic density planes. About 6 vol% residual SiO2 phase was present in the bulk of the Si2N2O ceramics. Current results have provided an important baseline for the understanding of the oxidation behaviour of Si2N2O. © 1998 Kluwer Academic Publishers