Papers by Author: Pavel Strunz

Abstract: Characterization of advanced materials by neutron powder diffraction provides information not accessible by other techniques. Thanks to the low absorption of neutrons, the bulk of the material and large-grain samples can be investigated, moreover in situ at elevated temperatures. The neutron diffraction use is demonstrated on two types of technologically important materials: Ti-Zr alloy and Co-Re high temperature alloy. In Ti-Zr alloy, the residual stress relief and microstrain evolution after ECAP was established. Boron influence on TaC strengthening precipitates in Co-Re high temperature alloys was shown not to be significant at the foreseen alloy operation temperatures, although boron content has a strong influence on the matrix phase.

Abstract: Single crystal Ni-base superalloys based on the  /  system are widely used in gas turbine applications. To understand the formation of  precipitates, including size distribution and growth, we performed in situ small-angle neutron scattering (SANS) measurements at elevated temperatures and - together with TEM as well as , SEM imaging - studied changes in the precipitates in short and long time scale. In the early stages, a bimodal precipitate size distribution of precipitate is observed, which (depending on the annealing temperature) changes to a cuboidal or nearly spherical morphology with almostmore or less uniform ( unimodal) size distribution. [Note: The term "more or less" is several times repeated in the text. I cannot imagine what it in fact means. Could you change it or explain in a more clear way]

Abstract: The creep degraded nickel base single crystal superalloy CMSX-4 of two axial orientations [001] and [111] was investigated with aim to assess the structure degradation. Constant load creep tests were conducted in the stress/temperature ranges of 250–780 MPa/750 – 50°C resulting in rupture time variation from 50 to 4000 hours. A combination of scanning electron microscopy (SEM) and non-destructive small-angle neutron scattering method (SANS) was used to investigate the directional coarsening (rafting) of the gamma prime (γ') precipitates in relation to the stress and temperature applied as well as to the initial crystallographic orientation of the specimens. The SANS results are discussed in terms of the correlation with the raft development, the axial orientation of specimen, the creep parameters and the mechanical properties.

Abstract: The modification of the Transformed Model Fitting /TMF/ [1] method developed for evaluation of the single-line profiles from high-resolution neutron powder diffractometers is proposed [2]. More sophisticated real-space model [3] is used for the distortion and crystallite size broadening of the diffraction lines. The new PC program based on this model has been tested on neutron diffraction profiles collected in situ upon tensile deformation tests of the plain ferritic steel. The deformation test was performed in the incremental mode in which each individual deformation step was followed by unloading. The neutron diffraction spectra were collected both upon loading and unloading and behavior of the diffraction profiles in elastic as well as in plastic region of the deformation curve was examined in detail. Comparison of microstress values in loaded/unloaded state and in elastic and plastic region offers interesting possibility to separate the contribution of the type II and type III microstresses.