Experimental investigation of Al2O3/8YSZ and CeO2/8YSZ plasma sprayed thermal barrier coating on diesel engine

In this research work, aluminium oxide/yttria stabilized zirconia (20%Al₂O₃/80%8YSZ) and ceria/yttria stabilized zirconia (20%CeO₂/80%8YSZ) were coated through atmospheric plasma spray technique (APS) as thermal barrier coating (TBC) over CoNiCrAlY bond coat on aluminium alloy (Al-13%Si) substrate piston crown material and their thermal cycling behavior were studied experimentally. Thermal cycle test of both samples were conducted at 800?°C. Microstructural, phase and elemental analysis of the TBC coatings were experimentally investigated. The performance, combustion and emission characteristics of Al₂O₃/8YSZ, CeO₂/8YSZ TBC coated and uncoated standard diesel engine were experimentally investigated. The test results revealed that CeO₂/8YSZ based TBC has an excellent thermal cycling behavior in comparison to the Al₂O₃/8YSZ based TBC. The spallation of the Al₂O₃/8YSZ TBC occurred mainly due to the formation of thermally grown oxide (TGO), and growth of residual stresses at top coating and bond coating interface. The experimental results also revealed that the increase of brake thermal efficiency and reduction of specific fuel consumption for both TBC coated engine. Further reduction of HC, CO and smoke and increase of NOx emission were recorded for both TBC coated engine compared to the standard diesel engine.     

Tensile flow and work-hardening behavior of a Ti-modified austenitic stainless steel

The flow-stress data of a 15Cr-15Ni-2.2Mo-Ti modified austenitic stainless steel in the temperature range 300 to 1023 K was analyzed in terms of Ludwigson and Voce equations. The parameters of these equations were critically examined with respect to the effect of Ti/C ratio and test temperature. It was found that the Ludwigson equation described the flow behavior adequately up to the test temperature of 923 K, whereas the Voce equation could be employed in the full temperature range. The peaks/plateaus observed in the variation of these parameters as a function of temperature in the intermediate temperature range have been identified as one of the manifestations of dynamic strain aging (DSA). Also, the variation of these parameters with temperature clearly could bring out the different domains of DSA observed in this alloy. The work-hardening analysis of the flow-stress data revealed that in the DSA regime, the onset of stage III hardening is athermal.     

Effect of silver on the formation of Bi2Sr2Ca2Cu3O10 (Bi-2 2 2 3) superconductors by sol–gel process

Bi-2 2 2 3 superconductors with silver additions are synthesized by sol–gel process. The effect of silver on the formation of Bi-2 2 2 3 phase is studied. The addition of silver brings down the reaction temperature as well as annealing time for the formation of Bi-2 2 2 3 phase. The presence of silver affects the Tc of the Bi-2 2 1 2 phase. The heat treatment of silver added Bi-2 2 2 3 samples above 1113 K show poor superconducting properties due to partial melting of Bi-2 2 2 3 phase. © 1998 Chapman & Hall