活化烧结工艺制备Ni-Cr/BN自润滑复合材料

以羰基Ni粉、Cr2O3和C粉为原料,添加六方BN（h-BN）作为固体润滑剂,采用粉末冶金活化烧结工艺制备Ni-Cr基自润滑材料（Ni-Cr／BN）。研究烧结温度、升温速度和保温时间对材料性能的影响,利用X射线衍射仪、金相显微镜、摩擦试验机和硬度计分析和测定材料的物相组成、显微组织、材料的摩擦磨损性能和硬度。研究结果表明：Ni-Cr／BN复合材料是以Ni-Cr合金作为基体,以Ni与Ni3B的低熔点共晶组织（熔点1097℃）作为粘结相;于1100℃保温1h可以制备孔隙度高达48％的Ni-Cr／BN材料,其布氏硬度为18,抗拉强度为24．8MPa,磨损率为74．4gg／min,平均摩擦因数为0．266。     

烧结温度对BN/Ni(Cr)自润滑材料组织与性能的影响

以Ni-20％Cr(质量分数)合金粉末作为基体材料,添加体积分数为31.4％的六方BN(h-BN)作为固体润滑剂,采用粉末冶金法制备BN/Ni(Cr)自润滑复合材料.研究不同烧结温度对该复合材料硬度、弯曲强度和孔隙率以及显微组织的影响.研究结果表明:BN/Ni(Cr)自润滑材料的硬度和抗弯强度与Ni-Cr颗粒烧结颈的形成、长大以及孔隙率的变化有关;当烧结温度不超过1 180℃时,随着温度的升高,BN/Ni(Cr)复合材料的孔隙率下降,硬度和弯曲强度均呈上升趋势.     

SiC/BN纳米复合陶瓷的高温氧化行为

采用循环氧化法对SiC／BN纳米复合陶瓷在1100℃和1300℃静态空气中的高温氧化行为进行了研究,研究结果表明在1100℃时,初期氧化时部分BN氧化成B2O3而挥发,产生较多的气孔,使其抗氧化性能降低。随着氧化反应的继续,氧化层（SiO2）的厚度增加,内部的BN不再继续氧化,只有SiC还可缓慢氧化。1300℃氧化时,由于SiC迅速氧化形成较为致密的氧化层,表面氧化膜均匀致密,并有晶相物在氧化膜中生成,可阻止内部的BN发生氧化,表现出较好的抗氧化性。     

铜基航空刹车材料的烧结温度与烧结压力

采用粉末冶金的方法制备一种新型铜基粉末冶金航空刹车材料,研究烧结压力和烧结温度对材料显微组织和致密化的影响以及由此引起的材料摩擦磨损性能和行为的改变。结果表明:当烧结压力由0.5 MPa增加到1.5 MPa时,材料的孔隙度显著减少,材料的摩擦因数明显减小,磨损性能得到显著改善;当烧结压力由1.5 MPa提高到2.5 MPa时,材料的孔隙度进一步降低,但降幅较小,材料磨损性能稍有提高;当烧结压力达到2.5 MPa以后,继续提高烧结压力对材料的致密化程度以及摩擦磨损性能影响不大;当烧结温度由900℃升高到930℃时,材料密度显著增加,材料的磨损性能得到显著改善;当烧结温度由930℃增加至1 000℃时,材料致密化程度进一步增加,但材料的磨损性能变化不大。     

化学镀法制备Ni—P／Al2O3特种陶瓷及性能

采用化学镀方法在平均粒径为200 nm的Al2O3粉体表面镀覆Ni-P合金,制备出了Ni-P/Al2O3复合粉体,再利用无压烧结将此种复合粉体制备成氧化铝基特种陶瓷。这一方法不仅降低了烧结温度,也进一步提高了陶瓷的性能,尤其是在提高韧性方面。结果表明,粉体镀层为晶态,主要由NiP2相和NiP相组成,镀层中含镍量为9.32%,含磷量为2.38%。为低磷合金镀层,制备特种陶瓷所需的烧结温度由制备单一氧化铝陶瓷所需的1 700℃降低至1 350℃;断裂韧性也从单一Al2O3陶瓷的3.0 MPa.m1/2提高到6.91 MPa.m1/2,增加了130.3%;耐磨性与纯氧化铝陶瓷相当。     

化学镀法制备Ni-P/Al2O3特种陶瓷及性能

采用化学镀方法在平均粒径为200 nm的Al2O3粉体表面镀覆Ni-P合金,制备出了Ni-P/Al2O3复合粉体,再利用无压烧结将此种复合粉体制备成氧化铝基特种陶瓷.这一方法不仅降低了烧结温度,也进一步提高了陶瓷的性能,尤其是在提高韧性方面.结果表明,粉体镀层为晶态,主要由NiP2相和NiP相组成,镀层中含镍量为9.32%,含磷量为2.38%.为低磷合金镀层,制备特种陶瓷所需的烧结温度由制备单一氧化铝陶瓷所需的1 700 ℃降低至1 350 ℃;断裂韧性也从单一Al2O3陶瓷的3.0 MPa·m1/2提高到6.91 MPa·m1/2,增加了130.3%;耐磨性与纯氧化铝陶瓷相当.     

Ni/SWNTs纳米材料抗氧化和电磁波吸收特性研究

为了提高单壁碳纳米管(SWNTs)的电磁波吸收能力,该文采用化学镀的方法在SWNTs表面镀覆一层金属镍。观察和分析了镀层的形貌、成分和微观结构。使用矢量网络分析仪测试了镀镍碳纳米管/石腊(Ni/CNTs/PAR)复合材料在8~18 GHz频率范围内的复介电常数和复磁导率。透射电镜观察结果和X-ray能量散射图谱表明SWNTs表面包覆了一层致密的金属镍;热重分析曲线显示表面镀镍处理将SWNTs的抗氧化温度从400℃提高到650℃;测得的电磁参数表明Ni/SWNTs/PAR复合材料在测试频域内具有良好的电磁介电性能;当该复合材料厚度为2.0 mm时,在低频的X波段(8.2~12.4 GHz)约有2.5 GHz的频域反射损失超过了10 dB,表明该复合材料在X波段具有良好的电磁波吸收性能。     

石墨表面镀镍对金刚石钻头胎体性能的影响

为了解石墨表面镀镍对金刚石钻头胎体性能的影响,采用热压烧结法制备了镀镍石墨/胎体复合材料,用扫描电镜观察石墨镀镍前后与胎体之间界面结合状态的变化,并研究了石墨表面镀镍对复合材料的抗弯强度、洛氏硬度以及在无冷却液的条件下与花岗岩对磨时的摩擦系数和磨损量的影响。结果表明:石墨表面镀镍之后,石墨与胎体之间的结合强度大幅度提高;提高了复合材料的整体性能,以及抗弯强度和硬度;增大了摩擦副的摩擦系数,且增大了胎体的磨损量。石墨表面镀镍提高了石墨/胎体复合材料的物理力学性能,但是降低了其干摩擦性能。     

基于氢化及O修饰对Gr/BN异质结性质的调控

采用基于密度泛函理论的第一性原理方法研究了氢化及层间O修饰对石墨烯/BN(Gr/BN)异质结结构稳定性和电子性质的影响.建立了上下表面氢化及层间存在O修饰的石墨烯/氮化硼异质结结构模型,计算了氢化及层间O修饰的异质结的能带结构、态密度及荷转移.研究发现,Gr/BN异质结的性质与石墨烯类似,带隙非常小,无法应用于电子器件...     

Ni/Zn扩散溶解层的初步研究

采用粉末烧结方法,利用光学显微镜、扫描电子显微镜、X射线衍射和能谱技术,研究了Ni-Zn体系固相烧结时粉末界面处形成的扩散溶解层的微观形貌和相结构,并利用TFDC电子理论讨论了扩散溶解层的形成机理.研究表明,Ni粉和Zn粉在200℃,15 h的烧结过程中,Zn原子不断扩散进入到Ni晶体中,在Ni粉颗粒基体上形成了由NiZn和Ni3Zn22金属间化合物构成的"带状"扩散溶解层.     

氮化硼薄膜的厚度对场发射特性的影响

利用射频磁控溅射方法, 在n型（100）Si基底上沉积了不同厚度（54~124 nm）的纳米氮化硼（BN）薄膜. 红外光谱分析表明, BN薄膜结构为六角BN（h-BN）相(1 380 cm^-1和780 cm^-1)结构. 在超高真空系统中测量了不 同膜厚的场发射特性, 发现阈值电压随着厚度的增加而增大. 厚度为54 nm的BN薄膜样品阈 值电场为10 V/μm, 当外加电场为23 V/μm时, 最高发射电流为240 μA/cm². BN薄膜场发射F-N曲线表明, 在外加电场作用下, 电子隧穿了BN薄膜表面势垒发射到真空.     

蒸发镀铝过程中铝液对蒸发舟表面腐蚀的研究

利用场发射扫描电子显微镜和电子能谱分析了工业应用中的二硼化钛/氮化硼导电陶瓷蒸发舟与金属铝液的反应.通过对蒸发舟与金属铝液接触面的显微形貌和成分分析得出该成分蒸发舟的失效机制为液态铝与舟体表面BN发生反应生成AlN,体积膨胀降低了导电相TiB2颗粒的连接,导致舟体电阻增加及发热不均匀,最后失效.对改善蒸发舟性能,提高其使用寿命提出了建议.     

Effects of BN content on the mechanical properties of nanocrystalline 3Y-TZP/Al2O3/BN dental ceramics

3Y-TZP/3wt％ Al2O3 powder was coated with varying amounts of BN using the urea and borate reaction sintering method, and then multiphase ceramics were prepared by hot pressing sintering. The micro-topography and the compositional analysis of synthesized ceramics were conducted through scanning electron microscopy, transmission electron microscopy and X-ray diffraction. A mechanical tester was used to analyze the Vickers hardness, fracture toughness, and bending strength of the synthesized ceramics. The results showed that the ceramic with a BN content of 12wt％ showed the best processability, but had diminished mechanical properties (such as fracture toughness and bending strength). The ceramic with a BN content of 9wt％ showed better processability than those with 3wt％ and 6wt％ BN. However, the fracture toughness was affected by the addition of 9wt％ BN, making this ceramic only usable as a base material for a three-unit fixed bridge. In con-trast, the ceramics with a BN content of 3wt％ or 6wt％ fulfilled the criteria for use in multi-unit restoration, but their low processability made them unsuitable for milling after sintering.     

Effects of BN content on the mechanical properties of nanocrystalline 3Y-TZP/Al_2O_3/BN dental ceramics

3 Y-TZP/3 wt% Al_2O_3 powder was coated with varying amounts of BN using the urea and borate reaction sintering method, and then multiphase ceramics were prepared by hot pressing sintering. The micro-topography and the compositional analysis of synthesized ceramics were conducted through scanning electron microscopy, transmission electron microscopy and X-ray diffraction. A mechanical tester was used to analyze the Vickers hardness, fracture toughness, and bending strength of the synthesized ceramics. The results showed that the ceramic with a BN content of 12 wt% showed the best processability, but had diminished mechanical properties(such as fracture toughness and bending strength). The ceramic with a BN content of 9 wt% showed better processability than those with 3 wt% and 6 wt% BN. However, the fracture toughness was affected by the addition of 9 wt% BN, making this ceramic only usable as a base material for a three-unit fixed bridge. In contrast, the ceramics with a BN content of 3 wt% or 6 wt% fulfilled the criteria for use in multi-unit restoration, but their low processability made them unsuitable for milling after sintering.     

Precipitation behavior of BN type inclusions in 42CrMo steel

Automobile crankshaft steel 42CrMo, which requires excellent machinability and mechanical properties, cannot be manufactured by traditional methods. To achieve these qualities, the formation behavior of boron nitride (BN) inclusions in 42CrMo steel was studied in this article. First, the precipitation temperature and the amount of BN type inclusions with different contents of boron and nitrogen in molten steel were calculated thermodynamically by FactSage software. Then the morphology and the size of BN type inclusions as well as the influence of cooling methods on them were investigated by scanning electron microscopy. Furthermore, the effects of cooling rate and the contents of B and N in molten steel on the morphology, size, and distribution of BN type inclusions were studied quantitatively and detailedly by directional solidification experiments. It is found that different BN inclusions in molten steel can form by controlling the cooling rate and the contents of B and N, which is important for obtaining the excellent machinability of 42CrMo steel.     

氮化硼(BN)纤维微结构与力学性能的关系

本文用电子显微术研究了BN纤维的微观结构，讨论了微结构对其力学性能的影响，提出了BN纤维制造工艺的改进方向。     

Superior machinability of steel enhanced with BN and MnS particles

The strategy that replacing part of MnS with BN was proposed in order to decrease the sulfur content in sulfur based free-cutting steel. The effects of BN and MnS inclusions on the microstructure and machinability of the steel were systematically investigated. The results show that most of the BN and MnS inclusions exist individually in the steel and only a small amount of them are in a composite state forming either isolated particles or clusters of particles. In the case of multi-phased steel, the theoretical calculation predicts that the volume of large BN particles should be 0.7 times of the volume of large MnS particles. The machinability of this type of BN and MnS alloy steel over a wide range of cutting speeds ranging from a low speed appropriate for drilling to a high speed appropriate for turning is confirmed as being equal to or superior to that of an MnS reference steel, even though the sulfur content in the composite steel is only half that of the MnS steel. The aptitude for cutting effect of 240 ppm nitrogen and 115 ppm boron in the composite steel is demonstrated to be equivalent or even better than 1000 ppm sulfur in MnS free-cutting steel.     

化学镀Ni-B/BN自润滑复合镀层研究

以制备具有自润滑性能的新型Ni-B/BN复合镀层为目的,研究了Ni-B/BN镀液配方及工艺条件,分析了镀液稳定性的影响因素,得到了耐磨性优于Ni-B镀层的Ni-B/BN复合镀层.Ni-B/BN复合镀层性能测试实验表明该复合镀层结合力好,具有优良的耐蚀、耐磨性.     

低碳含硼钢中BN的析出行为

以硼质量分数为0.0045%、氮质量分数为0.0039%的低碳含硼钢为研究对象,通过对实验钢在凝固过程中BN析出和长大的热力学与动力学进行分析,并结合实验研究了冷却条件对BN析出与长大行为的影响.结果表明：由于溶质元素B和N在凝固前沿的微观偏析,只有当凝固前沿的固相率大于临界值0.981时,BN才能在凝固前沿析出;在凝固前沿随着固相率的增加,B和N均具有明显的偏析.当固相率接近于1时,硼在剩余液相中的实际含量远高于氮元素的含量,氮的扩散是BN长大的限制性环节;钢液冷却速率的变化对B和N元素的偏析无显著影响,而生成BN的尺寸随着钢液冷速的增加而显著减小.