Ba-Nd复合变质对Mg-3Si-4Zn铸造合金组织及性能的影响

研究了Ba-Nd复合变质对Mg-3Si-4Zn铸造合金组织及力学性能的影响,用OM、SEM、EDS、XRD等方法对微观结构进行了表征,通过硬度测试研究了材料的力学性能。结果表明,当单一变质剂Ba在Mg-3Si-4Zn合金中的添加量为1.2%（质量分数）时,变质效果最好。形成的BaMg₂Si₂相可以作为初生Mg₂Si的异质形核核心,使初生Mg₂Si细化。Ba-Nd复合变质是通过在Mg-3Si-4Zn-1.2Ba合金中加入变质剂Nd来完成的。通过Miedema模型和对吉布斯自由能的线性拟合,发现由于Nd和/或Ba原子能与Si原子形成更加稳定的化合物NdSi、NdSi₂、Ba₂Si、BaSi₂,防止Si原子在凝固的初始阶段与Mg原子结合,因此初生Mg₂Si的生长速度被抑制,微观结构中初生Mg₂Si相变小。当Nd含量为2.0%时,Ba-Nd复合变质效果最好,即初生Mg₂Si由平均面积约为 600 μm² 的树枝状变为平均边长约5 μm的近似方形的组织,共晶Mg₂Si由平均面积约444 μm² 的复杂粗大汉字状变为平均面积约89 μm²的简单汉字状组织。合金硬度由575.75 MPa提高到612.11 MPa,提高了6.31%。     

化学镀镍复合添加剂BH的工艺特性

开发了一种由含钼化合物、碘化钾以及邻苯二甲酸酐衍生物组成的复合添加剂BH,讨论了它对化学镀镍液稳定性、镀速以及镀层磷含量、硬度、孔隙率和微观形貌的影响。对测试化学镀镍液稳定性的PdCl2试验标准进行了改进:温度由80°C提高到90°C,PdCl2的浓度由0.1g/L增加到1.0g/L。研究结果显示,新标准检验的镀液稳定性差异能较好地反映实际生产中的镀液稳定性差异;当复合添加剂BH的添加量为2.0mL/L时,化学镀镍层微观形貌得到较大的改善。经过新的PdCl2试验标准检验,该镀液可达到900s不发生浑浊,镀速为24μm/h,镀层孔隙率0.57个/cm2,磷含量7.3%,硬度520HV。     

提高硬铬镀层耐蚀性的双层镀铬工艺

以某型发动机的水泵轴为基体,在同一镀液和镀槽中电沉积制备乳白/光亮双层铬镀层。工艺流程为:前处理─装挂─入槽─镀乳白耐蚀铬─镀光亮耐磨铬─出槽─清洗─除氢─抛光─检验。镀液组成为:CrO3200~250g/L,H2SO42.2~2.6g/L,Cr3+离子2.0~3.5g/L。先在60~65℃、15~25A/dm2下施镀30min得到乳白铬镀层,随后在55~60℃、40~50A/dm2下施镀90min,即得乳白/光亮双层铬镀层。双层铬镀层的孔隙率比单层光亮铬镀层小,二者显微硬度相近,耐磨性优越。实际生产应用表明,双层铬镀层的耐蚀性优于单层光亮铬镀层。     

Nanoindentation of NiTi shape memory thin films at elevated temperatures

The shape memory effect and nanoindentation response of various phases of sputtered NiTi shape memory thin films were investigated as a function of temperature. The phase transformation temperatures of NiTi films were observed to be sensitive to a compositional shift. The mechanical properties of NiTi thin films also presented a significant response to phase transformations. At the same load, the maximum indentation depth for austenite is smaller than for martensite, indicating that martensite is softer than austenite. A martensite thin film was converted to austenite via in situ heating nanoindentation and displayed the mechanical properties similar to the austenite film at room temperature. These results underscore the validity of elevated temperature nanoindentation methods as a means of interrogating the mechanical properties of materials that undergo thermally-induced phase transformations. The details of the load–displacement curves are also described.     

高硬度聚氨酯灌封胶的制备及性能研究

以聚醚A、聚醚B、聚合MDI为原料,采用一步法合成了高硬度聚氨酯灌封胶,考察了聚醚配比、硬段含量、复配扩链剂配比对材料的硬度、拉伸强度、断裂伸长率、体积电阻率的影响。结果表明,随着聚醚A含量增加,材料的硬度、拉伸强度逐渐增加;体积电阻率先增加后减少,并在聚醚A和聚醚B的质量比为1：2时达到最大值;当复配扩链剂TMP和BDO质量比为1：2时,体积电阻率达4．8×10^16Ω·cm,材料的综合性能最佳,且可以满足市场需求。     

Development and machinability evaluation of MgO doped Y-ZTA ceramic inserts for high-speed machining of steel

ABSTRACT

In current high productivity manufacturing era, it is necessary to develop non-conventional newer tool materials. Here, an attempt has been made for developing MgO doped zirconia-toughened alumina (Mg-ZTA) using powder metallurgy process route. The 3 mol% yttria stabilized zirconia (YSZ) (10 wt%), alumina (Al₂O₃) (90 wt%) with varying percentage of magnesium oxide (MgO) (0–1 wt%) are mixed to study the phase transformation and uniaxially pressed into square inserts with 0.8 mm nose radius and sintered at 1,600ºC for 1 h in pressure less condition. The maximum hardness of 17.04 GPa, fracture toughness of 5.09 MPa m^1/2 and flexural strength of 502 MPa, respectively, has been reached at 0.6 wt% of MgO due to more metastable tetragonal phase. The performance of the insert has been evaluated by machining AISI 4340 steel (radius 75 mm) in lathe. The performance with respect to flank wear, cutting force and surface roughness is quite impressive at different cutting speed even after 20 min of machining. It can be inferred that MgO doped ZTA insert can be used for medium to high-speed machining in current manufacturing scenario and is very promising to replace carbide or coated carbide inserts in coming days.     

Cu/Ta/SiO_2/Si多层结构的纳米压痕研究

利用磁控溅射方法在Si衬底上沉积钽层以及铜层,并利用纳米压痕技术对Cu/Ta/SiO_2/Si多层膜结构进行了硬度和弹性模量的表征,研究发现多层膜结构的硬度随着薄膜厚度的增加而降低,然而弹性模量与膜厚之间并没有这样的关系。利用聚焦离子束（FIB）工艺将纳米压痕区域剖开,并通过透射电子显微镜（TEM）表征发现在纳米压痕过后,钽以及二氧化硅界面有了明显的分层现象,这一点表明层与层之间较弱的键合在相对大的负荷下遭到了破坏。     

铸渗工艺对刮板输送机铲板组织和性能的影响

采用涂料法在刮板输送机铲板表面渗硼、铬和碳以形成硬度较高的表面合金化层.通过改变合金粉末各自的比例来研究不同的涂料配比对表面合金化层组织和性能的影响.研究结果表明,表面合金化层内主要含有Fe-Cr,Fe₂₃(C,B)₆,Cr₂₃C₆、马氏体和莱氏体;当涂料的配比：B为10％,Cr为80％,C为10％时,表面合金化层的维氏硬度最高达到800 HV,刮板运输机铲板表面的维氏硬度提高了近3倍;试样的表面合金化层的厚度在8 mm左右,且随着B含量的增加维氏硬度逐渐下降.     

双尺度结构WC-12Co涂层的冷喷涂制备

以微米颗粒结构的传统WC-Co粉末为原料,采用球磨的方法,制备双尺度结构的WC-12Co粉末,采用冷喷涂方法制备双尺度结构WC-12Co涂层.通过扫描电镜观察发现,涂层及喷涂粉末中WC颗粒的粒度呈双峰分布.通过X射线衍射分析比较球磨前后粉末、喷涂粉末及涂层的相结构,发现在涂层制备过程中WC和Co两相结构能够在涂层中完全保留下来.涂层的硬度及断裂韧性分别为1650 Hv(0.3)和13.9 MPa.m1/2.