Effect of Rigid Inclusions on the Densification and Constitutive Parameters of Liquid‐Phase‐Sintered YBa₂Cu₃O_6+x Powder Compacts

Abstract

The presence of rigid inclusions in a powder compact leads to a reduction in the densification rate of the compact and may also lead to processing defects. In this paper, the densification rate and the constitutive parameters of both homogeneous YBa2Cu3O6+x and composite powder compacts (YBa2Cu3O6+x powder with 10 vol% dense inclusions of YBa2Cu3O6+x) are reported. A small amount of liquid phase, which formed during sintering, was present in the samples. However, even with the presence of a liquid phase, the addition of inclusions still reduces the densification rate of the composite and increases its viscosity. The results have been compared with a published analysis of the problem using measured values of the constitutive parameters. Both the viscosity and viscous Poisson's ratio of the porous body have been measured.

Constrained sintering: A delicate balance of scales

“…7. For solid state sintering, it exhibits a close to linear dependence on density, 104,109,113 ranging from about 0.2 at green density to 0.5 at 100% TD. The case of the LTCC material, however, appears to be quite more complex (Fig.…”

“…104,109 Application of a uniaxial load during hot forging can lead to anisotropy effects, thus thwarting good data for strain rates. This is particularly problematic for the determination of the viscous Poisson's coefficient, as its determination rests with the determination and then subtraction of small strain rates.…”

Uniaxial viscosity of low-temperature cofired ceramic (LTCC) powder compacts determined by loading dilatometry

“…The radial strain is negative at low stresses but positive (more apparent for the FA sample) at large stresses. Salamone et al 24 has addressed that it is due to Poisson's expansion in the radial dimension as a result of a compressive axial stress. Venkatachari 30 has explained that deformation strain dominates when the applied compressive stress is large enough, which leads to a positive value of the radial strain.…”

“…So far, extensive efforts have been carried out in order to determine the viscosity of a sintering body, and several models have been presented. 10,[12][13][14][15][16][17][18] Experimental techniques have also been used to determine the viscosity of a sintering body as a function of relative density, including loading dilatometry 15,16,[19][20][21][22][23][24][25] and optical dilatometry. 26 Among these methods, sinter-forging types of experiment are considered as a common approach, where a uniaxial load is applied on the cylindrical powder compact and, radial and axial strains are measured simultaneously.…”

Effects of heating history on sintering properties of nickel powder compacts

“…During the second step of two-step sintering, the mobility of the junctions may be lower than the grain boundary diffusion rate. The effects of the change in grain boundary/pore junctions on the driving force for densification has not yet been revealed, therefore, the effects of two-step sintering should be clarified from the view point of driving force as well as diffusion rate.Sinter-compression (forging) tests can be used to determine the sintering stress and the viscosity of powder compacts (Venkatachari and Raj, 1986;Rahaman et al, 1986; Zuo et al, 2003a), composites (Bordia andRaj, 1988;Salamone et al, 2003), glass (Ducamp and Raj, 1989), and metal/ceramic mixtures (Shinagawa, 2008(Shinagawa, , 2009. In these studies, microstructural evolutions, such as, grain growth, were considered, but no experiments have been done for the effects of heating history.…”