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High relative permittivity, ε r , over a very wide temperature range, −65 °C to 325 °C, is presented for ceramics designed to be compatible with base metal electrode multilayer capacitor manufacturing processes. We report a ≥ 300 °C potential Class II capacitor material, free from Bi or Pb ions, developed by doping Sr 2 NaNb 5 O 15 with Ca2+, Y3+ and Zr4+ ions, according to the formulation Sr 2−2z Ca z Y z NaNb 5-z Zr z O 15. For sample composition z = 0.025, ε r values are 1565 ± 15 % (1 kHz) from −65 °C to 325 °C. At a slightly higher level of doping, z = 0.05, ε r values are 1310 ± 10 % from −65 °C to 300 °C. Values of the dielectric loss tangent, tanδ are ≤ 0.025 from −60 °C to 290 °C, for z = 0.025, with tanδ increasing to 0.035 at 325 °C. Microstructural analyses exclude core-shell mechanisms being responsible for the flattening of the ε r –T response. [ABSTRACT FROM AUTHOR]

Abstract The effects of hydrogen on the mechanical properties of 304L keyhole tungsten inert gas welded joint were investigated in the study. The presence of hydrogen resulted in a significant decrease in the macroscopic ductility of the weld metal, and fracture may be initiated at the sites of clustered dislocations due to hydrogen atoms. Moreover, it is found that hydrogen may result in more severe loss in ductility and noticeable decrease in the flow stress and strength of the base metal, because of the interplay between the hydrogen atoms and strain-induced α′ martensite. Strain-induced α′ martensitic transformation and phase boundaries in the base metal may provide more sites for the accumulation of hydrogen and dislocations, leading to an appreciable decrease in the ductility and strength of the base metal. [ABSTRACT FROM AUTHOR]

Comparative fatigue tests were conducted on as-welded, weld toe peened specimens before and after fatigue loading. Fracture surface, residual stress, microstructure and hardness were determined. The test results showed that as the pre-fatigue loading period extended, deeper cracks may have initiated and propagated and the fatigue life improvement decreased. The processes of ultrasonic peening on welded joints with existing cracks were modeled by finite element analysis. The numerical results indicated that the mechanism of UIT improving fatigue performance included two factors: compressive residual stress and the change of crack orientation. Both effects reduced as the crack became deeper. [ABSTRACT FROM AUTHOR]