Diffusion Of Mn Research Articles

Investigation of in situ annealing effect on the thermal stability and crystallinity of IrMn thin films by X-ray diffraction and electron energy loss spectroscopy

The crystal reorganization of the IrMn thin film was observed by the in situ thermal annealing in the X-ray diffraction (XRD) and electron energy loss spectroscopy. From room temperature to 700 °C, the in situ annealing measurements identify the different Mn diffusion effects in three temperature ranges. First, between room temperature and 300 °C, the XRD profiles show the reorganization of Mn atoms from interstitials to IrMn lattice points. Second, between 300 and 400 °C, we observed the diffusion of Mn atoms from the IrMn thin film to the surface, causing the atomic Mn/Ir ratio to drop from 10 to 7. The MnO appeared on the film surface in this temperature range. Third, from 400 to 700 °C, the O content in the IrMn thin film increases to 8%, while the Mn/Ir ratio continuously decreases from 7 to 5. The scanning transmission electron microscopy images also show that the crystal structure of IrMn thin film completely degrades to another structure.

Interfacial Microstructure and Mechanical Properties of 1Cr18Ni9Ti/1Cr21Ni5Ti Stainless Steel Joints Brazed with Mn-Based Brazing Filler.

The problem of stainless steel brazing is still the focus of scientific research. In this work, the Mn-based brazing filler was used to braze 1Cr18Ni9Ti and 1Cr21Ni5Ti stainless steel. The typical microstructure of the 1Cr18Ni9Ti/1Cr21Ni5Ti joint was analyzed in detail, and the interface structure of the joint was determined to be 1Cr18Ni9Ti/Mn(s, s)/1Cr21Ni5Ti. The brazing temperature and holding time were shown to have a great influence on the microstructure of the brazed joint. The tensile strength of brazed joints first increased and then decreased with the rising of the brazing temperature and the holding time. The maximum tensile strength was 566 MPa when the joints were brazed at 1125 °C for 15 min. The diffusion of Mn and Cr was an important factor affecting the quality of the joints. The diffusion distances of Mn and Cr at different brazing temperatures and holding times were measured, and the diffusion activation energy and diffusion coefficient were achieved by the Arrhenius equation.

Mn diffusion in the ferritic Fe-25 %Cr Alloy: A First-principles study

The doping manganese (Mn) in the ferritic Fe-Cr alloy could effectively improve its high temperature performance when applied as metallic interconnects of solid oxide fuel cells (SOFCs). A theoretical study of Mn diffusion property in such alloy is implemented. It is found that the substitutional Mn atom prefers to diffuse along the 〈111〉 crystal direction with activation energy of about 0.40 eV. The interstitial Mn atom diffuses across the crystal between two tetrahedral interstitials with activation energy of about 1.37 eV. Under the working temperature of SOFCs at 600℃-800℃, the magnitude of diffusion coefficients mainly varies from 10-15-10-10m2/s which is qualitatively consistent with the experimental result that diffusion rate following the order of DMn > DCr. Our results reveal the diffusion mechanism of Mn atom in the ferritic Fe-Cr alloy at the atomic scale, which provide theoretical guidance for further applications of metallic interconnects in SOFCs.

Manganese phosphide nanoclusters embedded in epitaxial gallium phosphide grown from the vapor phase: Non-negligible role of Mn diffusion in growth kinetics

Orthorhombic MnP nanoclusters are formed in GaP epitaxial films grown by metalorganic vapor phase epitaxy on GaP(001) substrates, which are labeled as GaP:MnP/GaP(001). Polycrystalline MnP films have also been grown from the vapor phase on GaP substrates and are labeled as (p-c)MnP/GaP(001). Both GaP:MnP/GaP(001) epilayers and (p-c)MnP/GaP (001) films show a very rich texture, which has been previously characterized by three dimensional x-ray diffraction reciprocal space maps combined with transmission electron microscopy measurements. Heterostructures (HSs) containing multiple layers of (p-c)MnP/GaP and of GaP:MnP/GaP have been designed and grown with the same process. These HSs add new elements to our understanding of the growth mechanisms involved in these complex systems. In particular, it is shown that Mn diffusion during growth is strongly enhanced leading to a picture of MnP cluster coalescence, which explains some of their properties, such as the variation of their spatial distribution within the GaP matrix with the epilayer thickness. We report an Mn atomic diffusion coefficient of (1.5 ± 0.2) × 10−15 cm2/s in these films at 650 °C. The data are compatible with the superdiffusion of Mn, where the square of the diffusion length as a function of time (t) obeys λD2∝t1+α with an estimated value of α≈0.52.

Effect of B Segregation at Prior Austenite Grain Boundaries on Microstructures and Toughness in the Heat‐Affected Zone of Mg‐Deoxidized Shipbuilding Steel Plates

The effect of B segregation at prior austenite grain boundary (PAGB) on the microstructure and toughness in the heat‐affected zone (HAZ) after high heat input welding at kJ cm−1 for Mg‐deoxidized shipbuilding steel plates is clarified. With 0.0022 wt.% B addition, B segregation occurs at PAGBs in two forms: solute B and fine Fe23(BC)6 precipitates. B segregation with a concentration of about 4 at.% decreases boundary energy by 0.13 J m−2, which reduces the nucleation density of boundary ferrites by increasing the critical activation energy of ferrite nucleation. Thus, coarse grain boundary ferrites (GBFs) and ferrite side plates (FSPs) are suppressed with film‐like allotriomorphic ferrites formed at PAGBs, and ferrite transformation temperature reduces from 712–543 to 679–541 °C. In B‐free steels, (Fe, Mn)3C particles form at PAGBs with the Mn‐depleted zone (MDZ) at around (Fe, Mn)3C, promoting GBFs and FSPs. However, (Fe, Mn)3C precipitates and MDZ are not observed at PAGBs with B addition, because B segregation delays Mn diffusion to PAGBs. Thus, GBFs and FSPs reduce, and intragranular acicular ferrites (IAFs) increase with B addition, making the dislocation density and high‐angle grain boundary density increase, which improve HAZ toughness at −40 °C from 40 to 141 J.

Microstructural characterization and oxidation performance of solution-annealed and precipitation hardened wire-arc additively manufactured Inconel 718 superalloys

This research work investigated the effects of standard solution-annealed (SA) treatment on microstructure and chemical characteristics of Inconel 718 (IN718) superalloys fabricated using tungsten inert gas welding based wire-arc additive manufacturing (WAAM) process. A commercial wrought IN718 product was also studied for comparison. It was observed that WAAM parts developed highly-textured large columnar austenite (γ) grains along the build-up direction due to the epitaxy and high thermal dissipation rate. The micro-segregation of Nb produced an inhomogeneous γ-matrix precipitating non-hardening laves phases as a result of constitutional undercooling, high energy input and slow cooling rate of WAAM process. After the solution treatment, SA sample remained to be highly-textured solid-solution of γ-matrix and formed non-hardening delta (δ) plates with undissolved residual laves phases in Nb-enriched regions. These deprived the precipitation of beneficial hardening phases of γ″ and γ′ particles in γ-matrix during SA treatment. The high-temperature oxidation study of SA-treated samples obeyed parabolic rate law which was independent of oxidation temperatures. The oxidation mechanisms in the formation of oxide scale were found to be temperature dependent. At 800 °C, only a thin and continuous layer of Cr2O3 scale was formed externally at the air-alloy interface. A multi-layer of external Cr2O3 at air-scale interface, inner Nb-rich complex Ti0.67Nb1.33O4 scale at scale-alloy interface and internal sub-scale of Al2O3 was formed at 900–1000 °C. Due to the high lattice diffusivity of Mn+2 and Ti+4 cations through Nb-rich complex layer and Cr2O3 scale, a thin layer of TiO2 and MnCr2O4 was formed at the outermost part of Cr2O3 scale at 1000 °C. The oxidation reaction process of scale growth in IN718 alloys was mainly dominated by the outward diffusion of Cr+3 cations through Cr2O3 layer at the air-scale interface as the activation energies were found to be in the range of 250–290 kJ/mol for Cr2O3 (chromia) forming Ni-based superalloys.

Effect of the thermal field on the microstructure of dissimilar welded joints between TWIP steel and 2205 duplex stainless steel

This study reported a theoretical-experimental analysis of dissimilar metals duplex stainless steel (DSS) grade 2205 and twinning induced plasticity (TWIP) steel joined. Welded joints were performed in autogenous mode and using filler metal (ER2209) by the pulsed gas tungsten arc welding (GTAW-P) process. Critical weld regions were characterized metallographically using LOM and SEM. Microstructural changes such as the morphology and contents of ferritic and austenitic phases were correlated to the temperature ranges estimated numerically by a finite element (FE) model, which considered the variation of the percentage dilution in the fusion zone (FZ). The average variation between experimental and numerical results was up to 6.75%. SEM chemical analysis and line scanning analysis corroborated the diffusion of Al, Mn, Cr and Ni in the FZ of the autogenous joint. Small concentration gradients promoted a homogenous chemical composition of the ferritic and austenitic phases in the filler metal joint. The FZ exhibited an austenitic phase coarsening due to the elevated temperatures (1506°C–1803 °C, DSS 2205 side). Wetting problems were observed in both weldments producing prominent interfaces between the welded metal (WM) and the heat-affected zone (HAZ). Other weld defects such as underfilling, undercuts and lack of fusion were also detected. When a high TWIP steel volume was melted (filler metal joint), WM hardness increased compared to the autogenous joint. The hardness increment (2–5% in the DSS 2205) combined with the lack of fusion brought about the failure of the filler metal joint during the bend test.

Insight on precipitate evolution during additive manufacturing of stainless steels via in-situ heating-cooling experiments in a transmission electron microscope

During additive manufacturing of alloys, just after local heat-matter interactions, a molten material undergoes rapid solidification. Then, for the rest of the building time, it is subjected to cooling/heating cycles in the solid-state i.e., solid-state thermal cycling. The thermo-mechanical forces generated during solid-state thermal cycling can trigger a plethora of micro-mechanisms that can bring about significant microstructural changes that determine the eventual mechanical properties of as-built parts. In this work, the aim is to gain insight on solid-state thermal cycling-driven evolution of submicron-sized precipitates in an austenitic stainless steel using transmission electron microscopy. To that end, thin-film lamellae are extracted from a pre-built sample and subjected to different in-situ solid-state thermal cycles inside a transmission electron microscope. The solid-state thermal cycles are designed to understand the role of temperature amplitude and rate, number and type of thermal cycles, and post-process annealing on precipitate evolution. High angle annular dark field imaging and energy dispersive X-ray spectroscopy before and after each thermal cycle provide a deep insight on the contribution of different thermal cycling factors on the evolution of precipitate composition, size and morphology. Common trends include diffusion of Mn and Si from Mn-Si-rich oxides into the surrounding matrix, formation of Cr rings around oxide precipitates and S redistribution in non-oxide precipitates. Similar Cr rings and S distributions were also found in precipitates in as-built samples studied in (Upadhyay et al. [30]), which strongly supports the representativeness of these results with respect to what occurs during additive manufacturing.

On the mechanism of Mn partitioning during intercritical annealing in medium Mn steels

To understand how solute Mn in the reverted austenite is able to rapidly partition to near-equilibrium concentration values during the typically short intercritical annealing (IA) of medium Mn steels (MMS), reverse transformation kinetics were simulated numerically. We applied a variety of assumptions both for the diffusivity of Mn in austenite and martensite/ferrite and for the interface mobility. These simulation results were compared with measurements of the Mn concentration gradient near the interface as measured by atom probe tomography. Our inclusion of an interface mobility term, with physical origins from the interfacial dissipation energy, reduced the interphase interface migration rate, resulting in much higher values of the interfacial Mn concentration than in the scenario whereby diffusion-controlled transformation kinetics dominate. These results have led us to propose that the austenite/ferrite interface exhibits a fluctuational interface mobility during IA. This new phenomenological description of the interface migration achieves the best fit to the measured fluctuations of the Mn concentration gradients near the interface. We suggest that the fluctuational mobility arises from encounters between the interface and the regions of crystal containing precipitates and/or microstructural defects.

Colloidal Processing of Y0.08Zr0.92O2/La0.80Sr0.20MnO3 Semi-Cells Using a Sr-Doped Lanthanum Manganite Synthesized by a Citrate Route.

In this paper, the interface between yttria stabilized zirconia (Y0.08Zr0.92O2, YSZ) electrolyte and Sr-doped lanthanum manganite (La0.80Sr0.20MnO3, LSM) cathode for solid oxide fuel cells (SOFCs) is studied. For such a purpose, the combination of a suitable synthesis route for obtaining fine powders and simple aqueous colloidal shaping routes is proposed. The synthesis of nanosized particles of La0.80Sr0.20MnO3 by a citrate route and their full characterization, including the colloidal stability and the densification and phase development determined by X-ray diffraction and electron microscopy at different temperatures, is reported. In a second step, YSZ tapes were obtained by aqueous tape casting and used as substrates for the preparation of LSM coatings by dip-coating using aqueous slurries. YSZ tapes were used either in the green state or after a pre-sintering treatment. Co-sintering at 1350 °C led to a sharp interface with excellent adhesion, also achieved when coating pre-sintered tapes. In both cases, the substrates are dense and the coatings are porous, with thicknesses of 85 and 60 μm for green and pre-sintered tapes, respectively. No diffusion of Zr and Y occurs at the LSM layer, but some diffusion of La and Mn towards the YSZ layer takes place.

Heavy metals contamination, potential pathways and risks along the Indus Drainage System of Pakistan

Riverine water exposed to heavy metals (HMs) pollution is a major concern in the world because of its serious effects on ecosystem and human health. This study assessed the pollution status, sources, diffusion and potential risks of Mn, Co, Cu, Zn, Cr, Ni, Cd, Hg and Pb for the first time along the entire Indus Drainage System of Pakistan. The concentrations of nine HMs in the riverine water ranged from 5.05–101.59 μg/L with a mean value of 41.51 μg/L. The overall metals quantification along the drainage was significantly high (27% of the total) in River Chenab followed by River Indus (26%) > Soan (20%) > Ravi (19%) > Kabul (5%) > Swat (3%). The potential sources of contamination were identified to be the surrounding geogenic activities, industrial/municipal wastewater discharges, agricultural and surface runoffs by using multivariate statistics including metals correlation analysis, hierarchical cluster analysis and principal component analysis. The average mass flux of ∑HMs in the entire drainage was approximately 10.24 tons/year, to which the River Indus contributed 84% of the total, Chenab 11%, Ravi 3%, Kabul 1%, and Soan 1% with more prevalence of biological essential (Zn&Mn) and non-essential (Ni&Cr) metals. In terms of ecological risk, the riverine water metals contamination (1.59 to 57.06) was within the risk threshold (ERI < 110), while the risks of ∑carcinogenic metals for exposed children and adults along the basin were significantly influenced between acceptable to high cancer risk by Cd, Co, Ni, Cr and Pb.

Impact of magnetic transition on Mn diffusion inα-iron: Correlative state-of-the-art theoretical and experimental study

An accurate prediction of atomic diffusion in Fe alloys is challenging due to thermal magnetic excitations and magnetic transitions. We investigate the diffusion of Mn in bcc Fe using an effective interaction model and first-principles based spin-space averaged relaxations in magnetically disordered systems. The theoretical results are compared with the dedicated radiotracer measurements of $^{54}\mathrm{Mn}$ diffusion in a wide temperature range of 773 to 1173 K, performed by combining the precision grinding (higher temperatures) and ion-beam sputtering (low temperatures) sectioning techniques. The temperature evolution of Mn diffusion coefficients in bcc iron in theory and experiment agree very well and consistently reveal a reduced acceleration of Mn solute diffusion around the Curie point. By analyzing the temperature dependencies of the ratio of Mn diffusion coefficients to self-diffusion coefficients we observe a dominance of magnetic disorder over chemical effects on high-temperature diffusion. Therefore, the missing acceleration mainly reflects an anomalous behavior of the Mn solute in the magnetically ordered low-temperature state of the Fe host, as compared to other transition metals.

Microstructure-dependent phase stability and precipitation kinetics in equiatomic CrMnFeCoNi high-entropy alloy: Role of grain boundaries

The multi-principal element CrMnFeCoNi alloy, which solidifies as a single-phase solid solution with the face-centered cubic (fcc) structure, is thermally stable above 900 °C but is known to decompose into multiple phases at temperatures between 450 and 800 °C. Although the thermal stability of Cr-Mn-Fe-Co-Ni alloys can be altered by changing the composition, there is limited knowledge of the role of microstructure on the kinetics of precipitation from the supersaturated primary fcc phase. To fill this gap, we compared the thermal stability of monocrystalline and polycrystalline thin films of the equiatomic CrMnFeCoNi alloy during synthesis and after post-deposition annealing. At the processing temperature of 700 °C, the polycrystalline film undergoes substantial phase decomposition in 3 min, consistent with earlier results that a bulk alloy of similar composition decomposes into multiple phases at this temperature. In contrast, the monocrystalline film of the same composition remains single-phase both during synthesis and subsequent annealing at 700 °C for 5 h. X-ray diffraction investigations together with comprehensive transmission electron microscopy analysis revealed that the decomposition of the supersaturated primary phase is related to the presence of structural defects, in particular grain boundaries, which promote diffusion of Cr and Mn and subsequently destabilize the primary solid solution. Correspondingly, the absence of high-diffusivity grain boundaries in the monocrystalline alloy prevents its primary phase from decomposing. The fundamental role of grain boundaries on precipitation kinetics, manifested through the short circuiting of sluggish bulk diffusion in entropy-stabilized multi-principal element alloys, is discussed together with the possibility of controlling their thermal stability by microstructural design.

Surface Structure Analysis of Initial High-Temperature Oxidation of SS441 Stainless Steel.

Chromia-forming ferritic stainless steel (FSS) is a highly promising interconnect material for application in solid oxide fuel cells. In this study, initial oxidation of chromium oxides was performed at 500–800 °C to understand the evolution of materials at an early stage. The structural variations in oxide scales were analyzed through scanning electron microscopy, energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffractometry (XRD), laser confocal microscopy (LSCM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Surface electrochemical properties were investigated through electrochemical impedance spectroscopy to understand how the heat treatment temperature affected surface impedance. Treatment temperatures higher than 700 °C facilitate the diffusion of Cr and Mn, thus allowing ferritic spinels to form on the surface and leading to high electrical conductivity.

Manganese controlled transformation and twinning of the nanoscale austenite in low-carbon-medium-Mn steel

A Fe-10.5Mn-0.06C steel consisting of austenite and ferrite dual phases with a volume fraction ratio of 7:3 was fabricated via the quenching and partitioning (Q&P) processing. Tensile tests at various temperatures and strain rates were performed to reveal the mechanical properties of the steel, and the deformation microstructures were characterized by using TEM, t-EBSD and APT techniques. At a constant strain rate of 0.1 s−1, yield strength, tensile strength increase as the temperature decreases from 100 °C to −50 °C, and reach the highest values of 560 MPa and 1390 MPa at −50 °C, respectively. The specimens deformed at low temperatures (below 200 °C) exhibit a characteristic of three-stage work-hardening behavior, while those deformed at higher temperatures (200 and 300 °C) only show two-stage work-hardening curves. The extra hardening stage found at low temperatures is associated with the concurrent twinning and transformation in austenite with varying Mn contents as well as the interaction between twins and dislocations. With increasing temperature, the diffusion of Mn from austenite to ferrite is depressed, inhibiting the martensitic transformation. Consequently, the TRIP effect is weakened and the steel shows the reduced work-hardening rates at higher temperatures. In addition, a few nanoscale austenite residues (<200 nm) are remained even after −25 °C tensile deformtion, due to the highly localized Mn concentration of ∼15 wt%. These findings provide a guidance for designing advanced materials with combinations of ultrahigh strength and good ductility.

Tensile creep behavior and mechanism of CoCrFeMnNi high entropy alloy

As a potential novel superalloy, the study on the creep of high entropy alloys is of great significance. Equiatomic ratio CoCrFeMnNi with a mass of 6.7 kg was fabricated by vacuum induction levitation melting. Dendrite structure is obtained for as-cast alloy while a homogeneous equiaxed grain structure can be formed after annealing at 1273 K for 6 h. The tensile creep behavior of as-annealed alloy at 773–973 K and 50–340 MPa is systematically studied. Apparent dynamic recovery and recrystallization occur for creep at 973 K while high dislocation density can be observed for creep at 923 K and lower temperatures. Results of EDS analyses on fractured surface, stress exponent and activation energy for steady state creep rate suggest that the creep mechanism should be the dislocation viscous glide dragged by solute Mn at low stresses and low temperatures and be the dislocation climb associated with Mn diffusion at high stresses and high temperatures.

Mechanisms of austenite growth during intercritical annealing in medium manganese steels

The third-generation advanced high strength medium manganese (3–12 wt.%) steels typically consist of ultrafine-grained dual-phase (austenite-ferrite) microstructure, obtained through the intercritical annealing of martensite at temperatures typically ≤ 0.5Tmelt, where the bulk diffusion of Mn is extremely slow. Yet, the manganese partitioning plays a prominent role in the austenite growth from the martensitic matrix during this annealing step. Therefore, the ‘short circuit’ diffusion paths provided by grain boundaries (GBs) and dislocations must be crucial to the austenite growth. However, this influence is not well understood across the literature. In the present work, we study the mechanisms of austenite growth in a cold-rolled intercritically annealed medium manganese steel of composition Fe-10Mn-0.05C–1.5Al (wt.%). We provide evidence of manganese transport to austenite through GB diffusion, GB migration and dislocation pipe diffusion. Furthermore, the influence of GB misorientation on austenite growth is also reported.

Quantifying Mn Diffusion through Transferred versus Directly Grown Graphene Barriers.

We quantify the mechanisms for manganese (Mn) diffusion through graphene in Mn/graphene/Ge (001) and Mn/graphene/GaAs (001) heterostructures for samples prepared by graphene layer transfer versus graphene growth directly on the semiconductor substrate. These heterostructures are important for applications in spintronics; however, challenges in synthesizing graphene directly on technologically important substrates such as GaAs necessitate layer transfer and annealing steps, which introduce defects into the graphene. In situ photoemission spectroscopy measurements reveal that Mn diffusion through graphene grown directly on a Ge (001) substrate is 1000 times lower than Mn diffusion into samples without graphene (Dgr,direct ∼ 4 × 10-18 cm2/s, Dno-gr ∼ 5 × 10-15 cm2/s at 500 °C). Transferred graphene on Ge suppresses the Mn in Ge diffusion by a factor of 10 compared to no graphene (Dgr,transfer ∼ 4 × 10-16 cm2/s). For both transferred and directly grown graphene, the low activation energy (Ea ∼ 0.1-0.5 eV) suggests that Mn diffusion through graphene occurs primarily at graphene defects. This is further confirmed as the diffusivity prefactor, D0, scales with the defect density of the graphene sheet. Similar diffusion barrier performance is found on GaAs substrates; however, it is not currently possible to grow graphene directly on GaAs. Our results highlight the importance of developing graphene growth directly on functional substrates to avoid the damage induced by layer transfer and annealing.

Ordering mechanism and kinetics in Ni2Mn1−xCuxGa ferromagnetic shape memory alloys

The effect of atomic order on the martensitic and magnetic transformations undergone by Ni2Mn1−xCuxGa ferromagnetic shape memory alloys has been investigated. Different degrees of order have been induced by performing selected thermal treatments, and it has been found that, although both the structural (martensitic) and magnetic transformation temperatures increase with the improvement of the atomic order, each of these temperatures evolve with different kinetics. Reinforcing this result, during post–quench heating of Ni2Mn1−xCuxGa alloys two consecutive DSC exothermic peaks are observed, while the ternary Ni–Mn–Ga, Co–doped Ni–Mn–Ga and even Cu–doped Ni–Mn–Ga alloy when Cu replaces Ni show a single peak. The kinetics of the post–quench ordering processes have been studied using the Kissinger’s method, and two different activation energies have been obtained: 1.16 eV for the process that is common to all alloys and 1.35 eV for the one that is only observed in Ni2Mn1−xCuxGa alloys. The former, responsible for the change in Curie temperature, is attributed to the improvement of L21 order mainly due to Mn diffusion; for the second, which underlies the rise of martensitic transformation temperatures, diffusion of Cu atoms, misplaced in the Ni sublattice after quench, towards their most favourable sites in the Mn sublattice is proposed as the responsible mechanism.

Magnetic and structural properties of Mn5+xGe3+y thin films as a function of substrate orientation

Mn5Ge3 thin films were grown on GaAs(111) and GaAs(001) by Molecular Beam Epitaxy (MBE). The influence of stoichiometry and alloying of the samples was investigated using different Mn diffusion cell temperatures for each sample. X-ray diffraction (XRD) measurements reveal the following epitaxial relations: (001) Mn5Ge3//(111) GaAs and [110] Mn5Ge3//[2–1–1] GaAs for the sample grown on GaAs(111), and (111) Mn5Ge3//(001) GaAs and [−110] Mn5Ge3//[110] GaAs for the samples grown on GaAs(001). High-resolution transmission electron microscopy (HRTEM) results for a sample grown on GaAs(001) indicate that samples are around 70 nm thick and are composed of several grains with 2 different orientations corresponding to a 90° rotation around the [111] axis. Analyzing the Mn map with energy-filtered transmission electron microscopy (EFTEM) we observed that all the grains look very similar, indicating that they contain roughly the same amount of manganese. The magnetocaloric effect found in both family of samples is spread in a wider temperature range when compared with bulk Mn5.1Ge2.9 and the magnetic entropy change peak is higher than Si- or Sb- modified Mn5Ge3. This result makes the Mn5Ge3 a possible candidate for magnetic refrigeration while being a rare earth-free material.