http://localhost:8080/xmlui/handle/123456789/671 2010 Publications 2026-04-22T14:06:36Z http://localhost:8080/xmlui/handle/123456789/2605 Title: Effects of elemental additions (Si and Sb) on the ageing behavior of AZ91 magnesium alloy Authors: Srinivasan, A; Pillai, U T S; Pai, B C Abstract: Effects of Si and Sb additions on the ageing behavior of AZ91 alloy have been investigated. Additions of Si and Sb lead to the formation of thermally stable Mg2Si and Mg3Sb2 intermetallic phases, respectively, which are stable even after solution treatment at 410 ◦C for 48 h. Ageing treatment of AZ91 alloy at 200 ◦C results in the formation of Mg17Al12 phases in two morphologies: (i) discontinuous and (ii) continuous. Further the results of the present study have shown that individual and combined additions of Si and Sb suppress the formation of discontinuous precipitate during ageing. Dense populations of continuous precipitates observed around the hard intermetallic phases reduce the amount of chemical driving force required for both the initiation and propagation of discontinuous precipitates. In spite of these observations, the hardness measurements of aged alloy samples indicate that the alloying additions do not improve the peak hardness of AZ91 significantly 2010-09-25T00:00:00Z http://localhost:8080/xmlui/handle/123456789/2604 Title: Effect of intermetallic phases on the creep behavior of AZ91 magnesium alloy Authors: Srinivasan, A; Swaminathan, J; Gunjan, M K; Pillai, U T S; Pai, B C Abstract: Intermetallic phases play a major role in the creep behavior of Mg alloys. The effects of intermetallic phases on the creep behavior of AZ91 alloy have been studied in the present investigation. Thermally stable and finer intermetallic phases such as Mg2Si and Mg3Sb2 are introduced deliberately in AZ91 alloy by the addition of Si and Sb (0.5% Si, 0.5% Sb and 0.5% Si + 0.2% Sb, all are in wt%). Creep tests were carried out at 150 ◦Cand 200 ◦Cwith an initial stress of 50MPaon the as cast samples. The detailed microstructural analyses carried out on the crept samples indicate that the -Mg17Al12 intermetallic phase in the AZ91 alloy suffers sever cracking and facilities cavity formation due to its low melting point and incoherency with Mg matrix, which results in poor creep resistance. On the other hand, the creep behavior of AZ91 alloy at 150 ◦C is greatly improved with the presence of Mg2Si or Mg3Sb2 intermetallic phases because of their better thermal stability than Mg17Al12. These intermetallic phases strengthen the grain boundary against sliding and hence, reduce the possibility of void formation during creep. Furthermore, it also promotes more number of continuous Mg17Al12 dynamic precipitates near the grain boundary during creep, which in turn restricts the creep deformation 2010-03-15T00:00:00Z http://localhost:8080/xmlui/handle/123456789/2603 Title: Effect of Combined Addition of Nano-SiC and Nano-Ho2O3 on the in-Field Critical Current Density of MgB2 Superconductor Authors: Neson Varghese; Vinod, K; Chattopadhyay, M K; Roy, S B; Syamaprasad, U Abstract: MgB2 superconducting samples added with nano-Ho2O3 n-Ho2O3 and/or nano-SiC n-SiC have been prepared by an in situ solid state reaction method to investigate and compare the combined and individual effects of n-SiC and n-Ho2O3 on a crystal structure, critical temperature TC , and critical current density JC of MgB2. All the doped samples exhibit significantly enhanced in-field JC and the codoped sample with 2.5 wt % n-Ho2O3 and 5 wt % n-SiC gives the best performance in in-field JC, and the enhancement is around 100 times and 2 times greater than the undoped and monodoped n-SiC samples, respectively, at 5 K and 8 T. For the n-SiC added sample, lattice distortions due to C substitution on the B site and the formation of reacted phase Mg2Si as flux pinners cause enhanced JC up to the maximum field studied 8 T . While in the n-Ho2O3 added sample, a reacted phase HoB4 having a strong magnetic moment forms, without any substitution at the Mg or B site, which acts as a flux pinner in order to enhance the in-field JC. Accordingly the best codoped sample exhibits these combined benefits of n-SiC and n-Ho2O3 in MgB2 superconductor. © 2010 American Institute of Physics 2010-11-24T00:00:00Z http://localhost:8080/xmlui/handle/123456789/2602 Title: Effect of ZnO Doping on the Structural and Optical Properties of BaWO4 Thin Films Prepared Using Pulsed Laser Ablation Technique Authors: VENUGOPALAN PILLAI, N; VINODKUMAR, R; GANESAN, V; PETER KOSHY; MAHADEVAN PILLAI, V P Abstract: BaWO4 doped with ZnO (2, 3, 5, 7 and 10 wt%) nanostructured films are prepared on quartz substrates by pulsed laser ablation. The films are post annealed at 900 ◦ C. GIXRD analysis of the post-annealed films reveal the change of orientation of scheelite tetragonal crystal growth from 1 1 2 reflection plane to 0 0 4 planes when doping concentration is more than 3 wt%. The AFM images show that film with 7 wt% ZnO doping concentration has good ceramic pattern with surface features giving a minimum value of rms surface roughness suitable for optoelectronic device applications. The optical transmittance and band-gap energy of the films are found to decrease considerably on postannealing which can be due to the increase in grain size of the crystallites on annealing. Thus doping with ZnO improves the surface features of the films and increases the optical band-gap energy. 2010-12-01T00:00:00Z