Diffusion bonding by hot isostatic pressing (HIP) was performed between Incoloy 909 and five different ceramics. Two of the ceramics were composites made from powder mixtures of Si3N4 and either 60 vol% TiN or 50 vol% TiB2, while three were monolithic materials, namely Si3N4 with 2.5 wt% Y2O3 as a sintering additive, Si3N4 without additives, and Si2 N2O without additives. A diffusion couple geometry was developed to facilitate the preparation of thin-foil specimens for examination by analytical electron microscopy (AEM). Diffusion bonding was performed by HIP at 927°C (1200K) and 200 MPa for 4 h. The formation of reaction layers was very limited, being less than 1 μm in total layer thickness. Two reaction products were found by AEM; a continuous, very thin, (≤100 nm) layer of fine TiN crystals at the initial ceramic/metal interface, and larger grains extending about 100–500 nm into the superalloy and forming a semi-continuous layer of a G-phase suicide containing mainly nickel, silicon and niobium.

Large specimens of ceramic superconductors are difficult to solid-state sinter to full density, while maintaining superconductivity, without the high temperatures and pressures found in a hot isostatic press (HIP). HIPing can give highly dense, superconducting Bi2Sr2CaCu2O8 (Bi2212) and Bi2Sr2Ca2Cu3O10 (Bi2223) with only slight decomposition. If Y123 is HIPed to full density in a metal capsule, then the nonsuperconducting tetragonal phase forms as a result of decomposition. HIPing of CuO plus YBa2Cu3O7 gives highly dense, superconducting YBa2Cu4O8 (Y124), which is stable at high temperatures and oxygen pressures.

A new effect called ``ac-current straightening'' has been observed in ceramic (Bi,Pb)-2223 slabs carrying ac current Idc+Iac cos(ωt). The current-voltage (I-V) characteristics of the ceramic were measured at 77 K at frequencies ranging from 50 to 20 000 Hz. A spectrum analyzer showed a series of high harmonics in the voltage signal as well as a constant voltage drop. The full set of experimental data has been explained theoretically using the Bean-Kim critical state model with a magnetic field dependent critical current jc(H)=jc(0)/(1+H/H0). A low transport ac current gives a voltage linearly proportional to the frequency and quadratically proportional to the ac-current amplitude Iac. It consists of odd harmonics only. If a bias dc current is switched on, then even harmonics and a dc-voltage drop appear. Their amplitudes are proportional to the small parameter Iac/cH0 and depend on the Idc/Iac ratio.

We have measured the thermal conductivity κ and the thermal diffusivity a of a dense bulk ceramic polycrystalline sample of YBa2Cu4O8 (1:2:4) in the temperature range 30-300 K. We find κ≊10 W m-1 K-1 at 100 K, significantly higher than in ceramic YBa2Cu3O7-δ (1:2:3) and approaching the in-plane value for single-crystal 1:2:3, and decreasing to 7.6 W m-1 K-1 at 300 K. The data for this sample can be described by standard theories for phonon thermal conductivity of crystalline materials with boundary, phonon, and electron scattering. The higher κ in 1:2:4 as compared to 1:2:3 is, in this model, due to the smaller point defect scattering in the former. The fitted parameters for the three scattering mechanisms all agree with independent estimates based on simple models; inserting data for electric resistivity, grain size, carrier density, and lattice properties we can predict κ and its T dependence to within about 20%. We also discuss models for the phonon and electron thermal conductivities in some detail, including some second-order effects such as inelastic electron scattering and a T-dependent carrier density.

similarity in the dc voltage-current (V I) curves for both direct and alternating transport currents is used to propose that unpinned flux vortices are generated above the Ic transition for dc transport currents, when Abrikosov flux vortices begin to penetrate the superconductor. Two methods can be used to give a dc voltage drop for an ac transport current: (1) if there is a slight dc voltage in the ac current which favors vortex loop collapse as in a traditional dc Ic test, or (2) if an asymmetric transverse magnetic field is present which favors vortex loop collapse for current in one direction over the reverse direction.

The critical current Ic and the critical current density Jc of Bi-2223 phase bars have been found to depend on the mass density of the bars. Bars densified using a cold isostatic pressing (CIPing) process have been obtained with transport critical currents of gt;150 A with Jc levels up to approximately equals 103 A cm-2 at 77 K in the absence of an applied magnetic field. Bending or kinking of the grains may promote densification during CIPing of a sintered bar.

Hot isostatic pressed (HIPed) mixtures of Si3N4/60%TiN and Si3N4 /50%TiB2 were joined to Incoloy 909 (42%Fe, 38%Ni, 12.9%Cr, 4.7%Nb, 1.5%Ti, 0.4%Si) by hot isostatic pressing at 927 deg.C and 200 MPa. Microstructure (TEM and STEM) and diffusion profiles are reported and discussed. The work is relevant to the use of graded ceramics to reduce thermomechanical stresses in silicon nitride /superalloy joints

Diffusion reactions during solid state joining of a ceramic SiC/SiC composite to two superalloys, Hastelloy X and Incoloy 909, by hot isostatic pressing (HIP) have been investigated. The HIP pressure was 200 MPa in all joining cycles, and the temperature/dwell time were either 800°C/15 min, 900°C/1 h or 1000°C/1 h. The reaction zones formed consisted of a thin layer of carbides surrounded by several layers containing silicides and free carbon. The thicknesses of the reaction layers increased with increasing temperature, but were more affected by the composition of the alloy. With more carbide formers in the alloy, the thickness of the reaction layer decreased. The SiC composite was found to be considerably more prone to reactions with these superalloys during HIP as compared to Si3N4 under similar conditions