Song Xiaoguo

Reaction-Diffusion Bonding of High Nb Containing TiAl Alloy

Abstract In this study, high Nb containing TiAl alloy (TAN) was welded by reaction-diffusion bonding using Al foil as interlayer at 1200 °C for 2 h. The desired full lamellar microstructure ( γ +α 2 ) was obtained across the bonding seam when the joint was heat-treated according to the heat treatment process of TAN alloy. The present paper also investigated microstructure and bonding mechanism in details. The results show that liquid Al can react with TAN to form TiAl 3 intermetallic layer, and then the TiAl 3 layer will transform to γ -TiAl by solid-state diffusion at high temperature, finally a full lamellar structure is formed after heat treatment. Furthermore, sound joints with full lamellar structure can be also obtained when TAN alloy is directly bonded in accordance with the heat treatment cycle of TAN alloy.

A novel array calibration method based on spatial correlation matrix for HFSWR

This paper addresses a new method based on spatial correlation matrix to calibrate uniform linear array for HF Surface Wave Radar (HFSWR). Strong point echoes, such as target, clutter, transponder and so on, which are highly spatial correlated, can be used to structure spatial correlation matrix. And the matrix contains angles of echoes and phase errors information. In this paper, we use two-dimension FFT to estimate angle of strong point echo, and then obtain the corrections. Computer simulations and experimental results are conducted to show the validity of the new method.

复合活性钎料钎焊Cu与Al 2 O 3 的接头组织及性能

为改善紫铜与Al2O3陶瓷的连接强度，采用纳米-Al2O3增强的AgCuTi复合钎料(AgCuTip)对紫铜与Al2O3陶瓷进行了真空钎焊.采用扫描电镜、能谱分析以及剪切试验对钎焊接头微观组织及力学性能进行了分析.钎焊接头典型界面组织为紫铜/扩散层/铜基固溶体+银基固溶体+ Ti2Cu + Ti3(Cu, Al)3O/Al2O3.纳米-Al2O3的添加抑制了Al2O3侧反应层的生长，并促进钎缝中形成弥散分布的Ti2Cu相.随着保温时间的延长，铜侧扩散层和Ti3(Cu, Al)3O反应层的厚度逐渐增大.保温时间为20 min时，铜母材向钎料过度溶解，降低了接头性能.当钎焊温度为880 °C，保温10 min时，接头抗剪强度最高为82 MPa.纳米颗粒的加入细化了钎缝组织并降低了母材与钎缝热膨胀系数的不匹配，因此提高了接头的连接性能.保温时间可影响界面组织及反应层的厚度，进而影响接头的连接强度.