Weimin Gan

• PHD
• Researcher at Helmholtz-Zentrum Hereon

The textures of the β- and α-phases of the metastable β-titanium alloy Ti5321 after hot deformation were investigated by neutron diffraction. A hot-rolled bar was solutionized in the β-phase field and then hot compressed above and below the β-transus temperature. The initial texture after full recrystallization and grain growth in the β-phase field...

The main advantage of neutron diffraction over X-ray diffraction, arises from the fact that the interaction of neutrons with material is relatively weak and not related to the number of electrons, and consequently the penetration depth of neutrons is about 10²-10³ larger than that of laboratory X-ray diffraction. This is particular essential for th...

With neutron diffraction, the local stress and texture of metallic components can be analyzed non-destructively. For both, highly accurate positioning of the sample is essential, requiring the measurement at the same sample location from different directions. Current sample-positioning systems in neutron diffraction instruments combine XYZ tables a...

The strength–ductility trade-off has been a long-standing challenge when designing and fabricating a novel metal matrix composite. In this study, graphene-nanosheets (GNSs)-reinforced copper (Cu)-matrix-laminated composites were fabricated through two methods, i.e., the alternating electrodeposition technique followed by spark plasma sintering (SPS...

The interfacial stress-affected zone (ISAZ), characterized by a stress gradient maximizing at the interface, is considered a key factor in determining the mechanical properties of heterogeneous multi-layered materials. In the past few decades, the ISAZ dimension has been routinely estimated by two-dimensional strain mapping or by computational mode...

Generally, edge crack of rolled magnesium alloy sheets initiates in the RD (rolling direction)-ND (normal direction) plane and then propagate in the RD-TD (transverse direction) plane. Hence, the Mg-2Zn-1.5Mn (ZM21) alloy sheets with and without crack notch were designed to carry out in-situ tensile experiments under 150 °C (the same temperature of...

Laminates composed of varied thickness of Mg–Zn–Y alloy (ZW31) layers and (10 μm 15 vol. %) SiCp/AZ91 composite (PMMCs) layers were fabricated by hot extrusion and rolling in the present work. Then, the microstructure and mechanical properties of the laminates were investigated by adjusting the thickness ratio between the ZW31 layer and the PMMCs l...

Lightweight, high-modulus structural materials are highly desired in many applications like aerospace, automobile and biomedical instruments. As the lightest metallic structural material, magnesium (Mg) has great potential but is limited by its low intrinsic Young's modulus. This paper reviews the investigations on high-modulus Mg-based materials d...

CoCuFeMnNi complex concentrated alloy was subjected to hot compression at different temperatures and strain rates. Texture evolution for four representative samples was studied using electron backscatter diffraction, neutron diffraction and viscoplastic self-consistent simulations. EBSD revealed highest low angle grain boundaries and high angle gra...

An extraordinary high-strength dilute Mg-0.8Al-0.1Ca-0.6Mn (wt. %) alloy wire was successfully developed by hot drawing, which exhibits high tensile yield strength of 394 MPa, ultimate tensile strength of 431 MPa and moderate elongation to failure of 6.0%. The high strength was mainly attributed to the ultra-fine dynamically recrystallized (DRXed)...

Results are presented reporting on the martensite domain variant selection and stress-induced martensite morphology in [001]-oriented superelastic Co49Ni21Ga30 shape memory alloy (SMA) single crystals under tensile load. In situ neutron diffraction, as well as in situ optical- and confocal laser scanning microscopy were conducted focusing on three...

The effect of the heat treatment on the residual stresses of welded cladded steel samples is analyzed in this study. The residual stresses across the plate’s square sections were determined using complementary methods; applying diffraction with neutron radiation and mechanically using the contour method. The analysis of the large coarse grain auste...

Deformation of martensite twins is a prerequisite to obtain the shape memory effect in shape memory alloys, which is conventionally conceived to be realized by twinning/detwinning based on the simple shear. Here, we report the unconventional twin deformation of seven-layered modulated (7M) martensite under tension in a directionally solidified Ni50...

Previous investigations demonstrated that rare‐earth elements (REs) could improve their creep properties effectively. Herein, the influence of Y content on the creep properties of magnesium is investigated systematically with different amount of Y additions. The mechanisms responsible for creep deformation are clarified by the analysis of stress ex...

The B2-type intermetallic compounds CoZr and Co39Ni11Zr50 were deformed in tension at low temperatures. While CoZr is ductile down to 4 K, Co39Ni11Zr50 becomes brittle below 125 K due to a martensitic phase transformation. Thermal activation analysis shows that CoZr follows the Cottrell-Stokes law indicating forest dislocation cutting as the domina...

A modified quenching and deformation dilatometer is now in operation at the Heinz Maier‐Leibnitz Zentrum neutron center. It is customized for running neutron scattering measurements during the temperature/deformation treatment of the sample, in particular neutron diffraction (phase, texture, lattice strain) and neutron small angle scattering. Furth...

The effect of asymmetry deformation on microstructure and mechanical properties of AZ31 sheet was investigated in the present paper. Two AZ31 sheets were rolled together with an on-line heating rolling mill and separated from each other afterwards. For each sheet, the strain on both surface during rolling was asymmetry and this rolling method is ca...

An AlSi3.5Mg2.5 (wt%) alloy with excellent mechanical properties was produced via laser powder bed fusion in this study. The yield strength, tensile strength, and elongation of this as-built AlSi3.5Mg2.5 alloy reach about 406 MPa, 501 MPa, and 8.6%, respectively. These properties are dramatically superior to the current additively manufactured Al-S...

A modified quenching and deformation dilatometer (TA instruments DIL 805A/D/T) is now in operation at the Heinz Maier‐Leibnitz Zentrum (MLZ, Germany) neutron center. It is customized for running neutron scattering measurements during the temperature/deformation treatment of the sample, in particular neutron diffraction (phase, texture, and lattice...

Variant selection during phase transformation creates a specific transformation texture and finally affects the mechanical properties of the alloys. The transformation lattice deformation associated selection mechanism has not been well addressed. In the present work, the α variant selection in a Ti–7Mo–3Nb–3Cr–3Al alloy under isothermal compressio...

Anisotropic behavior is a key characteristic for understanding eccentricity in tubes. In this paper, the effect of using a tilted die during tube drawing on eccentricity, texture, dislocation density, and mechanical properties is shown. Copper tubes were drawn with a ±5° tilted die for two passes. The increase or decrease in eccentricity can be con...

Polycrystalline Ni50.4Mn27.3Ga22.3 alloy with <001> texture was prepared by conventional casting. The alloy exhibited enhanced magnetocrystalline anisotropy after superelastic training. Decent conventional magnetocaloric effect (MCE) with magnetic-field-induced entropy change ΔS = 9.2 J/kg·K under a magnetic field 30 kOe and inverse MCE with ΔS = 2...

The content of strain-induced martensite in austempered ductile iron has been quantitatively determined using three different kinds of neutron methods: (1) high-resolution powder diffraction with subsequent standard Rietveld refinement, (2) phase quantification using pole figure measurements and (3) Bragg edge neutron transmission. The accuracy and...

The AlSi10Mg alloy produced by laser powder bed fusion (LPBF) possesses a novel microstructure and higher mechanical properties compared with its casting counterpart. So far, the crystallographic orientation-dependent lattice strains, average phase stresses, and dislocation density during the tensile loading of the LPBF AlSi10Mg are not well unders...

The M40 carbon fibers reinforced magnesium matrix composites were fabricated by pressure infiltration method. The interfacial reactions and mechanical properties of the composites were optimized by adjusting the preheating temperatures of the preform (PRT) and the casting temperatures of the melting (CAT). The lower preheating temperatures of prefo...

The influence of amount of intermetallics on the degradation of as-extruded Mg-Nd alloys with different contents of Nd was investigated via immersion testing in DMEM+10% FBS under cell culture conditions and subsequent microstructural characterizations. It is found that the presence of intermetallic particles Mg41Nd5 affects the corrosion of Mg-Nd...

A Mg6Zn composite reinforced by novel urchin-like hybrid reinforcement of carbon nanotubes and silicon carbide ([email protected]) was fabricated via semisolid stirring assisted with ultrasonic vibration method and exhibits remarkable strengthening effect. Carbon nanotubes (CNTs) were in-situ and dispersed uniformly in the matrix with the assistanc...

Orientation related grain growth stimuli during primary and secondary recrystallization of the metal matrix in laminated metal/non-metal composites demonstrate unique effect on orientation evolution but has rarely been investigated. In this work, the recrystallization and grain growth of Cu in a graphene nanosheets (GNSs) reinforced laminated Cu ma...

The hybrid addition of CNTs was used to improve both the strengths and ductility of SiCp reinforced Mg matrix composites. A novel method was developed to simultaneously disperse SiCp and CNTs in Mg melt. Firstly, new [email protected] hybrid reinforcements were synthesized by CVD. Thus, CNTs were well pre-dispersed on the SiCp surfaces before they...

An interfacial CNT-(Mg-6Zn) layer was introduced between SiC particle and Mg-6Zn matrix by a novel method in aim to reduce the excessive thermal residual stresses between SiC particles and matrix. The CNTs were synthesized via CVD on the SiC surfaces, and CNTs kept on the surfaces of SiC particles in the composite during fabrication process. The in...

The microstructure and texture evolution of a metastable Ti–5Al–3V–3Mo–2Cr–2Zr–1Nb–1Fe alloy during bar-rolling and after various thermal treatments was investigated by high-energy synchrotron diffraction and electron backscatter diffraction. Bar-rolling is applied in the (α+β)-phase field in order to achieve a bi-modal (duplex) microstructure. The...

The effect of particle deformation zone (PDZ) on the microstructure and mechanical properties of SiCp/Mg-5Zn composites was studied. Meanwhile, the work hardening and softening behavior of SiCp/Mg-5Zn composites influenced by PDZ size were analyzed and discussed using neutron diffraction under in-situ tensile deformation. The evolution of FWHM (ful...

Arc welding generally introduces undesired local residual stress states on engineering components hindering high quality performance in service. Common procedures to reduce the tensile residual stresses are post heat treatments or mechanical surface treatments like hammering or shot peening. Assessment of residual stress profiles of post weld treat...

One of the most desired strengthening mechanisms in the carbon nanotube reinforced aluminum matrix composites (CNT/Al) composites is the load transfer strengthening mechanism (LTSM). However, a fundamental issue concerning the LTSM is that quantitative measurements of load partitioning in these composites during loading are very limited. In this st...

The present work studies the effects of solid solution Gd on the texture and lattice strain evolution of an extruded Mg15Gd alloy under uniaxial compression. In situ experiments were carried out using high energy X-ray diffraction on samples of the investigated materials with three different orientations. The original textures of the pure Mg and th...

Ni–Mn–Ga single crystal alloys can exhibit giant magnetic shape memory effect through variant reorientation induced by the magnetic field. However, such effect is greatly weakened in polycrystalline alloys, due to the orientation differences of martensite variants and the constraints of grain boundaries. Here, to improve the magnetic shape memory e...

The work hardening and softening behavior of pure Mg influenced by Zn addition were studied through the neutron diffraction at STRESS-SPEC under in-situ tensile deformation. The measurement of the line broadening evolution during in-situ tension was used to study the variation of dislocation density in pure Mg and Mg–5Zn alloy, which revealed the e...

A long-standing question is why layered structures can overcome the strength-ductility trade-off and achieve synergy in this relationship. In this paper, layered Ti/Al, Ti/Ti metal materials are taken as examples to investigate the influence of a heterogeneous layered structure on their deformation behavior from a viewpoint of the local strain. In-...

Single-crystal elastic constants have been derived by lattice strain measurements using neutron diffraction on polycrystalline Ti-6Al-4V, Ti-6Al-2Sn-4Zr-6Mo and Ti-3Al-8V-6Cr-4Zr-4Mo alloy samples. A variety of model approximations for the grain-to-grain interactions, namely approaches by Voigt, Reuss, Hill, Kroener, de Wit and Matthies, including...

Neutron diffraction measurements have been carried out for non-destructive characterization and numerical predictions validation of the residual stresses in a mock-up of the ITER-like divertor target plasma-facing component, made by hot radial pressing of 4 tungsten blocks to a CuCrZr cooling pipe via a soft copper interlayer. The neutron diffracti...

Diffraction is a powerful tool for analyzing residual as well as applied stresses. Both x ray and neutron diffraction can be used for this purpose. The interest in neutron stress analysis stems from the high penetrating power of neutrons when compared to laboratory x ray sources, i.e. several cm instead of a few tens of μm. This contribution will h...

In-situ synchrotron diffraction and atom probe tomography (APT) have been used to study the carbon diffusion and redistribution process in austempered ductile iron (ADI) during austempering. The process of carbon content change in bainitic ferrite during different austempering temperatures has been determined quantitatively. The transformation in A...

Cyclic stability is vital for the application of the elastocaloric effect. We demonstrated here the enhanced cyclic stability in a Ni 50.4 Mn 27.3 Ga 22.3 alloy via hot extrusion. The fine equiaxed grains with 〈111〉 A texture were obtained after hot extrusion at 1323 K. The extruded alloy showed >250 stable elastocaloric cycles without degradation....

N⁺ ion irradiation is utilized to tune the structure and mechanical properties of a Cu48Zr47.2Al4Nb0.8 bulk metallic glass composite (BMGC). Ion irradiation increases the disorder near the surface, as probed by neutron diffraction, and, moreover, causes the phase transformation from B2 CuZr to B19’ CuZr martensitic phase in the studied BMGC. The te...

The precipitation behavior of Mg-Al alloys during isothermal ageing has been investigated by dilatometry. Only continuous precipitation was observed in Mg-5.5Al during ageing at 175°C, 200°C, or 225°C, while both discontinuous and continuous precipitation occurred in Mg-8.9Al at the same ageing temperatures. Dilatometry curves showed that Mg-8.9Al...

The effect of second phases on the creep behavior of Mg-Ca-Zr alloys was investigated. Casting and hot-extrusion processes were performed to prepare Mg-xCa-0.5Zr (x = 0 wt.%, 0.3 wt.% and 0.6 wt.%) alloys with different morphologies and distributions of second phases. The as-cast microstructures of Mg-Ca-Zr alloys consisted of an Mg matrix and coar...

Shape memory alloys, especially the newly developed Ni–Mn-based heusler-type intermetallic compounds, exhibit specific mechanical responses to mechanical loading. Although the deformation behaviors have been studied for reducing the number of martensite variants, the mechanisms are not fully revealed. Thus in this work the compression process of tw...

High precision dimensionality tubes are required for a number of applications. Nevertheless, there are some troubles and challenges to produce high quality tubes in a cost-effective way. In recent works done at the Institute of Metallurgy at Clausthal University of Technology, the tube drawing process was optimized by introducing dynamic tilting an...

The materials used in superconducting magnet coils and in the structural magnet constituents are textured to various extents. This causes an angular dependence of the Young's moduli that needs to be taken into account when predicting the stress and strain distribution in the magnets. We have measured by neutron diffraction the texture in metallic m...

The Nb <sub xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn superconductor in accelerator magnets must resist high mechanical stresses. In order to better understand the effect of the coil impregnation system on the stresses exerted on the strain-sensitive Nb <sub xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn superconductor, we have m...

The effects of welding speed on the macroscopic and microscopic residual stresses (RSes) in friction stir welded 17 vol.% SiCp/2009Al-T4 composite plates were studied via neutron diffraction and an improved decoupled hierarchical multiscale modeling methods. Measurements showed that the macroscopic and total RSes had the largest variations in the l...

Many phase transformations produce crystallographic variants. Under a mechanical constraint, certain variants could be selected. Although efforts have been made on resolving the selection rule, the transformation lattice deformation associated selection mechanism has not been well addressed. Thus in the present work, α variant selection of the β to...

This paper presents a non-destructive evaluation method of volumetric texture using resonant ultrasound spectroscopy (RUS). It is based on a general theoretical platform that links the directional wave speeds of a polycrystalline aggregate to its texture through a simple convolution relationship, and RUS is employed to obtain the speeds by measurin...

Crystallographic texture in polycrystalline materials is often developed as preferred orientation distribution of grains during thermo-mechanical processes. Texture dominates many macroscopic physical properties and reflects the histories of structural evolution, hence its measurement and control are vital for performance optimisation and deformati...

The metallurgical texture of several of the gold artefacts found in 1998 at a Bronze Age fortification near Bernstorf in Bavaria was studied by neutron diffraction using the STRESS-SPEC instrument at the FRM II reactor of the Maier-Leibnitz Centre of the Technical University of Munich. The pieces consist of approximately 0.1 mm-thick gold sheets em...

The influences of Nd content on microstructures, mechanical properties and tension-compressing yield asymmetry at room temperature were investigated on extruded pure Mg and Mg-Nd binary alloys. Nd in the range of 0.05-0.63 at.% has been added to pure Mg. The grain sizes of the Mg-Nd alloys decreased with increasing Nd content. In particular, the gr...

Elastocaloric cooling is currently under extensive study owing to its great potential to replace the conventional vapor-compression technique. In this work, by employing multiscale characterization approaches, including in situ neutron diffraction in a loading frame, in situ transmission electron microscope observation at different temperatures, in...

Layered Ti-Al metal composite (LMC) was designed and fabricated by hot-rolling and annealing of pure Ti and Al sheets. The as-prepared composite exhibits high tensile ductility, being superior to any individual Ti or Al sheets. The stress/strain evolution and fracture behavior of the LMC were analyzed by in-situ observations during the tensile defo...

The present work attempts to reveal the correlation between the microstructural defects and residual stress in the single crystal nickel-based superalloy, both of which play the significant role on properties and performance. Neutron diffraction was employed to investigate the microstructural defects and residual stresses in a single crystal (SC) n...

Metallic tubes usually show heterogeneities along circumference and through wall thickness. Local texture analysis by synchrotron diffraction and global texture analysis by neutron diffraction was used describing texture variations related to the wall thickness. Test sample was an SF-Cu tube with outer diameter of 140 mm and an average wall thickne...

Among all alloying elements the rare earth elements (RE) play a key role in improving the ductility, high temperature strength and corrosion resistance effectively for magnesium and its alloys. The present work investigated the influences of single alloying or multi heavy REs (Gd, Dy and Y) alloying on the strengthening and ductilizing of magnesium...

A model for the strain-induced martensitic transformation in austempered ductile iron (ADI) has been developed based on neutron diffraction studies. Quantitative phase analysis was carried out using the Rietveld method including texture analysis. The key parameters applied in this model that influence the strain-induced martensitic transformation a...

Evolutions of texture and lattice strain of swaged brass samples were investigated by neutron diffraction at STRESS-SPEC under tensile deformation using a unique tension/compression rig. The two phased sample BS1 (61% α-brass and 39% β-brass) became 100% α-brass after 400 °C annealing (sample BS2). The starting texture of the as-received material B...

In this study, lithium gradients forming in the graphite anode of a commercial 18650-type lithium-ion battery during discharge and the associated relaxation processes after discharge were monitored by neutron diffraction. The experiments reveal the coexistence of several Li1-xC6 phases with different lithium contents during discharge, which can be...

An intensive formation of crystal defects in the α-Al matrix of an as-cast Sr-modified eutectic Al–Si alloy, induced by heat treatment with rapid heating, has been studied. This phenomenon arises from the fragmentation of the Si crystals and the diffusion of Al atoms into the cracks of the Si crystals. During the rapid heating process, a large temp...

The high flux neutron diffractometer STRESSSPEC at FRM II, Garching Germany, offers a flexible instrument setup suitable for fast and surface residual strain measurements. Likewise bulk, local or gradient texture analyses are feasible. Here improvements of the hardware (detector, slits) of the instrument as well as developments on methods for resid...

The evolution of the internal strains during in situ tension and compression tests has been measured in an MgY2Zn1 alloy containing long-period stacking ordered (LPSO) phase using neutron diffraction. The alloy was extruded at two different temperatures to study the influence of the microstructure and texture of the magnesium and the LPSO phases on...

In this Reply we demonstrate that the nano domains reported in our paper commented by D. Banerjee cannot be the artifacts induced by hydrogen absorption from electropolishing, as assumed by D. Banerjee. The effects of two different TEM sample preparation methods (ion milling and electropholishing) were verified and compared with some results in the...

This study investigates the effects of the extrusion ratio and annealing treatment on the microstructure, texture and mechanical properties of an as-extruded Mg–11Gd–4.5Y–1Nd–1.5Zn–0.5Zr (wt%) alloy. A high extrusion ratio (30:1) results in a homogeneous microstructure with fine dynamic recrystallized (DRXed) grains, while a low extrusion ratio (6:...

For the β phase of Ti-5553-type metastable β-Ti alloys, striations in transmission electron microscopy (TEM) bright- and dark-field images have been frequently observed but their origin has not been sufficiently investigated. In the present work, this phenomenon is studied in depth from the macroscopic scale by neutron diffraction to the atomic sca...

Heusler type Ni-Mn-Ga ferromagnetic shape memory alloys can demonstrate excellent magnetic shape memory effect in single crystals. However, such effect in polycrystalline alloys is greatly weakened due to the random distribution of crystallographic orientation. Microstructure optimization and texture control are of great significance and challenge...

Twinning in extruded AZ31 alloy with a bimodal grain structure is studied under compression along the extrusion direction. This study has combined in-situ measurements during the compression tests by Synchrotron Radiation Diffraction and Acoustic Emission techniques and the evaluation of the microstructure and texture in post-mortem compression sam...

Solid-state refrigeration based on the caloric effects is promising to replace the traditional vapor-compressing refrigeration technology due to environmental protection and high efficiency. However, the narrow working temperature region has hindered the application of these refrigeration technologies. In this paper, we propose a method of combined...

The β to α phase transformation of Ti alloys progresses in a displacive-diffusive mixed-mode. The associated transformation strain has important influence on the resultant microstructure. In this work, the microstructural features of α precipitates in a metastable β Ti alloy, Ti-7333, were thoroughly investigated. Special attention was paid to the...

Mg and its alloy have large potential in weight reduction usages because of their low density. However, the relatively low strength and modulus hinder their widely applications. Accumulative roll bonding (ARB) is one kind of severe plastic deformation (SPD) process which can produce bulk ultrafine-grained (UFG) metallic materials. In order to impro...

TiAl based alloys are desirable materials for turbine blades in aircraft engines. Depending on alloy composition and temperature additionally disordered β-Ti(Al) (A2 structure) or ordered β o -TiAl (B2 structure) can occur. Unfortunately little is known about the exact order/disorder transformation temperatures of β/β o . We used the good contrast...

In the last decades, there have been significant advances in texture measurement techniques and analyzing software. This chapter introduces various texture measuring techniques, from laboratory machines to large facilities. By comparing the characteristics of each method, a guideline to a more effective use for different research purposes is provid...

In this study local texture of process vessels made of carbon steel cladded by protective layers of stainless steel by submerged arc welding (SAW) were investigated by neutron diffraction using the diffractometer STRESSSPEC at FRM 2 (Garching, Germany). Different samples were prepared: as welded and as welded plus relevant industrial heat treatment...

A new Mg-RE (rare earth) alloy was previously developed by micro-alloying method (RE< 0.4 wt.%), which achieves a high ductility and good corrosion resistance. In-situ tensile test via neutron and synchrotron diffraction were performed to investigate first the deformation behaviour; and second the texture evolution which can be related to the defor...