Multiple Wavelengths Texture Measurement Using Angle Dispersive Neutron Diffraction at WOMBAT

Abstract

In contrast to conventional angle dispersive neutron diffractometers with a single-tube detector or a small-size linear position-sensitive detector, the WOMBAT diffractometer of the Australian Nuclear Science and Technology Organisation (ANSTO) is equipped with a large-area curved position-sensitive detector, spanning 120° for the scattering angle 2θ and 15° for the azimuth η, respectively. Here, WOMBAT was employed in establishing a texture measurement environment for complex textured samples, through measuring neutron diffractograms at two selected wavelengths on a typical reference sample of martensite–austenite multilayered steel sheet. All neutron patterns were simultaneously Rietveld analyzed using the software, Materials Analysis Using Diffraction (MAUD). The shorter wavelength (λ1 = 1.54 Å, k1 = 4.08 Å−1) enabled collecting the martensite reflections α-110, α-200, α-211, α-220, α-310, and α-222, as well as the austenite peaks γ-111, γ-200, γ-220, γ-311, γ-222, and γ-331 simultaneously, by pre-setting the detector range to 2Θ = 30~150°. The longer wavelength (λ2 = 2.41 Å, k2 = 2.61 Å−1) enabled separating the overlapping strong martensite α-110 and austenite γ-111 Laue–Bragg interferences more reliably. Moreover, the detector panel division along the vertical direction has a good stereographic coverage in the azimuthal angle η,. Such a combination of multiple-wavelength neutron diffraction combined with simultaneous Rietveld texture analysis was confirmed as being very valuable for realizing high precision measurements for complex textured samples at an orientation distribution graticule of 5°, and in a much shorter beam time than the conventional angle dispersive method.