Enhanced Thermoelectric and Mechanical Properties of n-type Bi_2Te_(2.7)Se_(0.3) Bulk Alloys by Electroless Plating with Cu

Bi_2Te_(2.7)Se_(0.3)/Cu core/shell powders were prepared by electroless plating and hydrogen reduction, and then sintered into bulk by spark plasma sintering in order to improve the thermoelectric and mechanical properties of n-type Bi-Te thermoelectric material. After electroless plating, with the increasing of Cu content, Seebeck coefficient keeps increasing and power factor enhances significantly. The highest power factor increases by three times and reaches 23.8 W·cm-1·K-2 at room temperature in Bi_2Te_(2.7)Se_(0.3) with 0.22 wt%Cu sample, which means electrical transport properties of Bi_2Te_(2.7)Se_(0.3)/Cu samples have been improved.Meanwhile, the ZT values of Bi_2Te_(2.7)Se_(0.3)/Cu samples can be enhanced at different temperature zone by adjusting the Cu content. Bi_2Te_(2.7)Se_(0.3) with 0.05 wt% Cu sample has the best thermoelectric properties in high temperature zone, and the ZT peak value increases from 0.35 to 0.85 at 623 K. When the Cu content increases to 0.15 wt%,the ZT peak value moves to the low temperature(373 K) and increases from 0.24 to 0.71. At the same time, the mechanical properties increases with the increasing of Cu content.     

Effects of Electroless Plating with Cu Content on Thermoelectric and Mechanical Properties of p-type Bi<Subscript>0.5</Subscript>Sb<Subscript>1.5</Subscript>Te<Subscript>3</Subscript> Bulk Alloys

Bi_0.5Sb_1.5Te₃/Cu core/shell powders were prepared by electroless plating and hydrogen reduction, and then sintered into bulk by spark plasma sintering. After electroless plating, with increasing the Cu content, the electrical conductivity keeps enhancing significantly. The highest electrical conductivity reaches 3341S/cm at room temperature in Bi_0.5Sb_1.5Te₃ with 0.67wt% Cu bulk sample. Moreover, the lowest lattice thermal conductivity reaches 0.32 W/m·K at 572.2 K in Bi_0.5Sb_1.5Te₃ with 0.67wt% Cu bulk sample, which is caused by the scattering of the rich-copper particles with different dimensions and massive grain boundaries. According to the results, the ZT values of all Bi_0.5Sb_1.5Te₃/Cu bulk samples have improved in a high temperature range. In Bi_0.5Sb_1.5Te₃ with 0.15wt% Cu bulk sample, the highest ZT value at 573.4 K is 0.81. When the Cu content increases to 0.67wt%, the highest ZT value reaches 0.85 at 622.2 K. Meanwhile, the microhardness increases with increasing the Cu content.     

Effects of Electroless Plating with Cu Content on Thermoelectric and Mechanical Properties of p-type Bi_(0.5)Sb_(1.5)Te_3 Bulk Alloys

Bi_(0.5)Sb_(1.5)Te_3/Cu core/shell powders were prepared by electroless plating and hydrogen reduction, and then sintered into bulk by spark plasma sintering. After electroless plating, with increasing the Cu content, the electrical conductivity keeps enhancing significantly. The highest electrical conductivity reaches 3341 S/cm at room temperature in Bi_(0.5)Sb_(1.5)Te_3 with 0.67 wt% Cu bulk sample. Moreover, the lowest lattice thermal conductivity reaches 0.32 W/m·K at 572.2 K in Bi_(0.5)Sb_(1.5)Te_3 with 0.67 wt% Cu bulk sample, which is caused by the scattering of the rich-copper particles with different dimensions and massive grain boundaries. According to the results, the ZT values of all Bi_(0.5)Sb_(1.5)Te_3/Cu bulk samples have improved in a high temperature range. In Bi_(0.5)Sb_(1.5)Te_3 with 0.15 wt% Cu bulk sample, the highest ZT value at 573.4 K is 0.81. When the Cu content increases to 0.67 wt%, the highest ZT value reaches 0.85 at 622.2 K. Meanwhile, the microhardness increases with increasing the Cu content.     

化学镀Sn含量对p型Bi0.5Sb1.5Te3块体合金电传输及力学性能的影响

通过化学镀和氢气还原法制备Bi_(0.5)Sb_(1.5)Te_3/Sn核壳结构粉末,再使用放电等离子烧结的方法制备成块体。经试验分析发现,随着Sn含量的上升,Seebeck系数和电导率均先上升后下降,含有1%(质量分数)Sn的Bi_(0.5)Sb_(1.5)Te_3/Sn块体合金的Seebeck系数上升至278μV/K,电导率略低于未镀层样品,为475.6 S/cm。因此,室温下的功率因子从24.6 W·cm~(-1)·K~(-2)提高到35.4 W·cm~(-1)·K~(-2),这证明样品的电传输性能得到提高。此外,随着Sn含量的上升,Bi_(0.5)Sb_(1.5)Te_3/Sn块体合金的密度及显微硬度不断升高,力学性能得到提高。     

铸镁壳体零件封孔修复技术研究

铸造镁合金壳体不同程度地存在缩孔、沙眼等内部缺陷,易出现工作液渗漏.该类渗漏有渗漏量小、渗漏点多、难以精确定位等特点,用焊接等技术难以根本解决问题.针对此问题,采用与壳体相同材料的铸镁合金制作试样,自制封孔剂,使用刷涂的方法封孔,并结合产品特点制定了工艺流程.通过试验表明,试片表面粗糙度越高,封孔剂与基体的结合力越好.封孔后试样的耐油性和耐蚀性都较好.验证性试验证明,封孔后壳体的性能可以满足实际使用的要求.优化后的工艺操作简单,且满足产品质量要求,可直接应用于特殊环境下铸镁合金壳体封孔修理,具有很好的经济效益和技术应用前景.     

金相磨抛工艺对碳化钨涂层组织评定的影响

碳化钨涂层内部为复合相组织,硬度高脆性大,金相制备易导致涂层内部出现裂纹、分层、拔出等缺陷。本文利用超音速火焰喷涂制备WC-10Co-4Cr涂层,采用不同的金相研磨和抛光工艺,分别评定WC-10Co-4Cr涂层的组织。结果表明:不同的金相研磨和抛光工艺对WC-10Co-4Cr涂层的孔隙率的评定结果有明显影响。随着磨抛压力的上升,涂层内部孔隙的尺寸明显增大,涂层原有孔隙周边被压裂、脱落,且脱落碳化钨颗粒进一步增强了对涂层表面的磨削效果,使得涂层表面的局部区域出现大范围脱落,从而导致随着研磨压力的上升,涂层的孔隙率升高了12.5%至30%,随着抛光压力的上升,涂层的孔隙率升高了近一倍。因此,为降低磨抛工艺对涂层组织评定的影响,建议使用15N的磨抛压力开展碳化钨涂层的金相制备,以获得更加准确的金相评定结果。