Ni–Cr–Al Alloy for neutron scattering at high pressures

Abstract

High-pressure devices used in neutron scattering require materials with high strength, low neutron attenuation, and no activation. They should also be non-magnetic. Only very few materials fulfil these criteria. Here, it is reported on the manufacture and properties of the Ni–Cr–Al alloy (57.0 wt-% Ni, 40.0 wt-% Cr, and 3.0 wt-% Al). The casting and heat treatment to obtain the material with the optimal yield strength are described in detail. Synchrotron powder diffraction reveals that phases of the Ni2Cr, Cr, and Ni3Al types are present. Aging has no significant effect on their lattice parameters and volume fractions. The alloy has no magnetic order down to at least 1.9 K as evidenced by magnetic measurements and diffraction with polarised neutrons. This paper is part of a Thematic Issue on The Crystallographic Aspects of Metallic Alloys.

Clamp cells for high pressure neutron scattering at low temperatures and high magnetic fields at Heinz Maier-Leibnitz Zentrum (MLZ)

“…As already indicated earlier [3], the Ni-Cr-Al alloy transmits fewer neutrons than CuBe2 (Figure 6).…”

“…The locking nuts (32 mm in diameter) have inner M20 threads. The cylinder and locking nuts are made of either Berylco 25 (B25 HT, NGK Berylco France), called CuBe2 in the following text, or the Ni-Cr-Al alloy (NiCrAl) [3]. The yield strength (σ) of fully hardened CuBe2 is 1.1 GPa at 300 K, while for NiCrAl it is in the range 1.7-2.4 GPa depending on aging [3,8].…”

“…Combined pressure-temperature neutron scattering studies are challenging as usually large samples (several mm 3 in size) are required. At the same time, the dimensions and the weight of the pressure cell are limited by the available cryostat capacity.…”

“…The pressure cell should also be non-magnetic down to very low temperatures to be used for polarized neutron scattering to reveal weak magnetism. Only a few high-strength materials satisfy these criteria [2][3][4].…”

Combined X-ray and neutron single-crystal diffraction in diamond anvil cells

“…Alternatively, the M3 and M4 bolts can be made of high-tensile titanium alloys (Klotz, 2013). The DAC can also be produced from Ni-Cr-Al alloy ('Russian alloy', NiCrAl), which has superior mechanical properties compared with CuBe (Cheng et al, 2019). Unlike most of the materials that are used to manufacture DACs for X-ray diffraction, CuBe and NiCrAl are ideal for both X-ray and neutron diffraction as they are non-magnetic down to very low temperatures and weakly attenuate neutrons.…”