Damping mechanisms of Fe–Mn alloy with (γ + ɛ) dual phase structure

Abstract

The objective of the present study is to propose damping mechanisms for Fe–Mn alloys containing austenite (face centred cubic) and ? martensite (hexagonal close packed), and to analyse the individual contribution of damping mechanisms to the total damping capacity of an Fe–17 wt-%Mn alloy with respect to volume fraction of ? martensite. On the basis of substructural characteristics of γ and ? phases, it is suggested that damping mechanisms of Fe–Mn alloys with (γ + ?) dual phase structures involve stress induced movement of various boundaries such as stacking fault boundaries in austenite and ? martensite, ?martensite variant boundaries, and γ/? interphase boundaries. The damping capacity of the Fe–17Mn alloy increases with increasing ? martensite content. The quantitative analysis shows that in the as quenched state, the ? martensite phase is responsible for a major part of the damping capacity.     

Strength evaluation of α and β phases by nanoindentation in Ti–15Mo alloys with Fe and Al addition

Abstract

The strengths of the α precipitate and the β matrix were evaluated by nanohardness in the Ti?15Mo?1Fe and Ti?15Mo?3Al alloys and compared to those of the Ti?15Mo alloy. The α phases with similar size (a long axis of a few micrometres and a short axis of a few hundred nanometres), distribution and volume fraction were obtained in three alloys by adjusting the aging temperature. Analyses by SEM-EDS confirmed that Fe and Mo were enriched in the β phase and depleted in the α phase, while Al was enriched in the α phase and depleted in the β phase. Tensile tests were carried out, and the tensile strength was shown to be higher in the Ti?15Mo?1Fe and Ti?15Mo?3Al alloys than in the Ti?15Mo alloy. The nanohardness measurements indicated that the α phase was softer than the β phase in both Ti?15Mo?1Fe and Ti?15Mo alloys, while it was harder in the Ti?15Mo?3Al alloy. The increased tensile strength was mainly caused by the strength of the Fe enriched β phase in the Ti?15Mo?1Fe alloy and by the strength of the Al enriched α phase in the Ti?15Mo?3Al alloy.     

Structures and magnetic properties of overaged Fe-AI-Mn-C alloys

Abstract

Microstructures and magnetic properties in the aged hardened Fe-9AI-30Mn-x(C,Si) alloy, during overaging at 823 Kfor 48 h to 313 days, have been investigated by transmission electron microscopy, X-ray diffraction line profiles, and vibrating sample magnetometry. The results reveal that the precipitate k phase ((Fe,Mn)₃AIC) decomposition in this alloy, overaged at 823 k for one week, proceeded by two separate mechanisms; (a) wetting of the½α_o′<100> antiphase boundary segment of D0₃ ((Fe/Mn)₃Al) domains by B2 ((Fe/Mn)Al) phase, and (b) precipitation of B2 ((Fe/Mn)Al) structure within the domain. A similar superparamagnetic behaviour was discovered when the alloy was overaged at 823 K for 120-313 days. The super soft magnetic properties were mainly attributed toferromagnetic B2 ((Fe/Mn)Al) domains, D0₃, and ;α′-Mn phases.     

Effects of Thermally Induced Cyclic γ ↔ ε Transformation on Shape Memory Effect of a Quenched FeMnSiCrNi Alloy

The effects of thermally induced cyclic γ ? ε transformation on microstructures and shape memory effect (SME) are investigated in a quenched Fe14Mn5.5Si8.0Cr5.0Ni alloy. The results show that the annealing at 773 K remarkably improves the SME in the quenched alloy. One thermal cycling between 290 and 773 K remarkably increases the SME, but the further thermal cycling hardly improves the SME. The reason is that the amount of thermal ε martensite remarkably reduces after annealing at 773 K, but it hardly changes with the further increase of thermal cycling between 290 and 773 K. The pre‐existing thermal ε martensite not only prevents the occurrence of stress‐induced ε martensitic transformation but also promotes the formation of α′ martensite.     

Effect of heat treatment on microstructure and mechanical properties of Cu–6.9Ni–2.97Al–0.99Fe–1.06Mn alloy

ABSTRACT

The effect of heat treatment on the mechanical properties and microstructures of Cu–6.9Ni–2.97Al–0.99Fe–1.06Mn alloys was investigated. The results show that the microstructure of the as-cast alloy mainly consists of an alpha-copper matrix and γ-phase Ni₃Al particles. The microstructure of the alloy after solution treatment at 950°C for 2?h is a single-phase alpha-copper supersaturated solid solution and the second-phase strengthening disappears. After ageing treatment at 550°C for 6?h, the γ-phase particles are fully precipitated, and the mechanical properties of the alloy are significantly improved. The tensile strength is increased from 305 to 588?MPa. Quasi-cleavage fracture with shallow dimples appeared in the Cu–6.9Ni–2.97Al–0.99Fe–1.06Mn alloy aged at 550°C for 6?h.     

Effect of alloying elements on properties and microstructures of Ti–V–Cr burn resistant alloys

Abstract

Burn resistant Ti alloys have been developed over the last 10 years. The aim of the present paper is to study the effects of alloying elements on properties and microstructures of Ti–V–Cr burn resistant alloys. The alloys Ti–35V–15Cr, Ti–25V–15Cr, and Ti–25V–15Cr–3Al usually show simple β phase structures, and recrystallisation finishes at 800°C. The Ti–25V–15Cr alloy has good workability, tensile properties, and thermal stability compared with the Ti–35V–15Cr and Ti–25V–15Cr–3Al alloys. There are α precipitates in the Ti–25V–15Cr alloy after exposure at 500°C for 100 h, which leads to a decrease in the thermal stability.     

Effects of Cr on stacking-fault energy and damping capacity of FeMn

Effects of Cr on the stacking-fault energy (SFE) and damping capacity were investigated by experimental and theoretical methods. The effect of Cr on SFE was thermodynamically calculated; the damping capacity, phase composition, microstructure and corrosion resistance were experimentally measured. The results showed that Cr increases the SFE of Fe17MnxCr which resulted in the decay of damping capacity; the increase in α’ martensite with the increasing Cr content above 6% pins the movement of Shockley partials’ dislocation and thus makes the damping capacity even worse; the optimum Cr content of Fe17MnxCr to improve the corrosion resistance in water vapour with a lesser decrease in damping capacity is about 6%.     

Guest Editorial: Personal perspective on microstructure of steels: 25th anniversary of MST and collection of papers in honour of Sir Robert Honeycombe

Abstract

The shape memory properties and microstructure associated with γ(fcc) → ?(hcp) martensitic transformation in an Fe–14Ru alloy have been investigated. The degree of shape recovery was measured via a bending test, and the microstructure was examined using X-ray diffractometry, optical microscopy, and transmission electron microscopy. The Fe–14Ru alloy showed shape recovery to some extent, but to a lower degree than in Fe–Mn–Si based shape memory alloys. The lower strength of the matrix, the presence of ? and α′ martensites at room temperature, and the higher stacking fault energy in the Fe–14Ru alloy are thought to be responsible for the weaker shape memory effect.     

Tensile elongation of lean-alloy austenitic stainless steels: transformation-induced plasticity versus planar glide

An Fe–13Cr–3.4Mn–0.47C lean-alloy stainless steel was made austenitic by solution annealing at 1250°C. Tensile tests between 20 and 200°C indicated enhancement of ductility at higher temperatures. At 200°C where planar glide, manifested as deformation twinning, was the dominant deformation mechanism, a uniform tensile elongation of 102% was achieved. At 20°C where deformation-induced α′-martensitic transformation replaced deformation twinning as the dominant deformation mechanism, tensile elongation was significantly impaired. The tensile elongation contribution by the planar glide was estimated to be at least four times that of the α′-TRIP (transformation-induced plasticity) mechanism. The results indicate that inexpensive lean-alloy austenitic stainless steels exhibiting pronounced α′-formation at room temperature could become highly formable at higher temperatures.     

Reversible structural relaxation of amorphous Ni70TM5Si10B15 (TM = V,Cr, Mn,Fe, Co,Ni) alloys

The structural relaxation of amorphous Ni₇TM₅Si₁₀B₁₅ (TM = V, Cr, Mn, Fe, Co, Ni) alloy was investigated by the electrical resistance measurement under isochronal annealing. The reference Ni₇₅Si₁₀B₁₅ alloy showed no reversible changes in electrical resistance. All alloys other than TM = Ni exhibited a reversible change which is peculiar to the chemical short-range ordering. Only in TM = Cr alloy was the reversible part predominantly observed after pre-annealing, and in other alloys the irreversible change was also seen. The degree of reversible change below 623 K was in the order Fe > V > Cr > Co > Mn. This origin is discussed on the basis of Ni-TM correlation, which is considered to play an important role in ordering, and TM-metalloid correlation, which is considered to hinder the formation of an ordered phase.     

Role of alloying elements in microstructures of beta titanium alloys with carbon additions

Abstract

The effect of 0.2 wt-%C on the microstructure of beta titanium alloys Ti-15X(Fe, Cr, Mn, Mo, Ni, Co, Cu, and V) has been studied using scanning and transmission electron microscopy. It has been found that coarse eutectic TiC_x tends to be formed in beta titanium alloys containing Fe, Cr, Mo, and Mn, and relatively finer homogeneous TiC_x is formed in alloys containing V, Ta, Co, Ni, or Cu. The volume fraction of TiC_x in alloys containing Cu, Co, and Ni is much less than that in other beta titanium alloys. The oxygen content of the matrix is lower than that of Ti₂C in Cr or alloys containing Mn and higher than that of Ti₂C in alloys containing Mo or Ni. These observations are discussed in terms of the role of phase diagrams and the effect of atomic radius of alloying elements on the dimension of interstitial sites in the host alloy and the sublattice of TiC_x.     

Nanostructured electrode materials for Ni-MH x batteries prepared by mechanical alloying

Nanocrystalline TiFe- and Mg₂Ni-type alloys were prepared by mechanical alloying followed by annealing. The structure and electrochemical properties of these materials were studied. The properties of hydrogen host materials can be modified substantially by alloying to obtain the desired storage characteristics. It was found that the respective replacement of Fe in TiFe by Ni and Mn improved not only the discharge capacity but also the cycle life of these electrodes. On the other hand, a partial substitution of Mg by Mn in Mg_2?x M _x Ni alloy leads to an increase in discharge capacity, at room temperature. Furthermore, the effect of the nickel and graphite coating on the structure of the nanocrystalline alloys and the electrodes characteristics were investigated. In Mg₂Ni-type alloy mechanical coating with graphite effectively reduced the degradation rate of the studied electrode materials.     

Fabrication and oxidation resistance of nanocrystalline Fe10Cr alloy

Nanocrystalline (nc) and microcrystalline (mc) Fe10Cr alloys were prepared by high energy ball-milling followed by compaction and sintering, and then oxidized in air for 52 h at 400 °C. The oxidation resistance of nc Fe10Cr alloy as determined by measuring the weight gain after regular time intervals was compared with that of the mc alloy of same chemical composition (also prepared by the same fabrication route and oxidized under identical conditions). Oxidation resistance of nc Fe10Cr alloy was found to be in excess of an order of magnitude superior than that of mc Fe10Cr alloy. This article also presents results of secondary ion mass spectrometry (SIMS) of oxidized samples of nc and mc Fe–Cr alloys, evidencing the formation of a more protective oxide scale in the nc alloy.     

Application of damping mechanism model and stacking fault probability in Fe–Mn alloy

In this paper, the damping mechanism model of Fe–Mn alloy was analyzed using dislocation theory. Moreover, as an important parameter in Fe–Mn based alloy, the effect of stacking fault probability on the damping capacity of Fe–19.35Mn alloy after deep-cooling or tensile deformation was also studied. The damping capacity was measured using reversal torsion pendulum. The stacking fault probability of γ-austenite and ε-martensite was determined by means of X-ray diffraction (XRD) profile analysis. The microstructure was observed using scanning electronic microscope (SEM). The results indicated that with the strain amplitude increasing above a critical value, the damping capacity of Fe–19.35Mn alloy increased rapidly which could be explained using the breakaway model of Shockley partial dislocations. Deep-cooling and suitable tensile deformation could improve the damping capacity owning to the increasing of stacking fault probability of Fe–19.35Mn alloy.     

Properties and application of Fe–6Si–14Mn–9Cr–5Ni shape memory alloy

Abstract

Three iron based shape memory alloys were studied and Fe–6Si–14Mn–9Cr–5Ni alloy showed the best shape memory effect. By thermomechanical training, the shape memory effect was improved and an absolute recovery strain of 6·2% was obtained. To promote the ε→γ transformation, which is not complete even after heating the alloy to 1000 K, the As and Af temperatures are decreased and the transformation enthalpy is increased by thermal cycling and increasing prestrain. The alloy also shows good creep and stress relaxation resistance. In addition, under a tensile force of 20 kN and a sealing test pressure of 6 MPa pipe joints made using the alloy remain effective and can satisfy the requirements for possible industrial applications.     

Isothermal embrittlement of Fe–8Mn alloys at 450°C

Abstract

Two Fe–8Mn alloys, one of which is alloy 193, stabilised with 0·17%Ti and 0·18%Al, were austenitised at 900°C, ice brine quenched and their DBTTs determined. In this condition, brittle fractures were predominantly cleavage, and thermodynamic calculations on alloy 193 showed that there were 0·0025 wt-%C and <0·03 ppm N in solid solution. Alloys were tempered for 6 min, 1 h and 10 h at 450°C and their DBTTs again determined; in this case, brittle fractures were mainly intergranular. In alloy 193, DBTT rose from 27 to 125°C in 6 min. Hardness values at 450°C were also monitored and the variation of hardness with time is discussed. It is thought that brittle fracture in alloy 193 is due to segregation of Mn per se to prior austenite grain boundaries, unlike an earlier investigation of a pure Fe–8Mn alloy (K1525), where embrittlement was due to a Mn–N and to a lesser extent a Mn–P interaction at prior austenite grain boundaries. The driving force for Mn segregation to prior austenite grain boundaries is thought to be the initial formation of reverted austenite at such sites.     

Deformation behavior of duplex austenite and ε-martensite high-Mn steel

Abstract

Deformation and work hardening behavior of Fe–17Mn–0.02C steel containing ε-martensite within the austenite matrix have been investigated by means of in situ microstructural observations and x-ray diffraction analysis. During deformation, the steel shows the deformation-induced transformation of austenite → ε-martensite → α′-martensite as well as the direct transformation of austenite → α′-martensite. Based on the calculation of changes in the fraction of each constituent phase, we found that the phase transformation of austenite → ε-martensite is more effective in work hardening than that of ε-martensite → α′-martensite. Moreover, reverse transformation of ε-martensite → austenite has also been observed during deformation. It originates from the formation of stacking faults within the deformed ε-martensite, resulting in the formation of 6H-long periodic ordered structure.     

Precipitation Processes in Al-Mg-(Mn,Cu) Type Alloy Sheets Evaluated Through Electrical Resistivity Variations

Precipitation/dissolution processes were followed by electrical resistivity variations in Al-Mg-(Mn)-Cu and Al-Mg-Mn type alloy sheets after different thermo-mechanical treatments (TMTs). In order to get an insight into the precipitation processes during processing of Al-Mg type alloys, some samples were solution treated at 535°C/1 h, and some of them were recrystallization annealed at 320°÷350°C/3 h. After that all the samples were treated in a same manner: cold rolling to 50–60% and final annealing at temperatures in the range of 220°÷470°C/3 h. It was supposed that the structure of samples pre-treated by recrystallization annealing at 320°/350°C is characterized with S type (Al₂MgCu) phases in the Al-Mg-(Mn)-Cu alloys and with β′/β (Mg₅Al₈) phases in the Al-Mg-Mn alloys. These structure features are rather unchangeable during the subsequent cold rolling and annealing treatments in the temperature range of 220°÷320°C. During annealing at higher temperatures (such as 470°C) precipitation of Mn-bearing particles (MnAl₆ or (Fe,Mn)Al₆) might occur in both type of alloys. After solution treatment at 535°C most of the alloying elements are dissolved into solid solution, thus inducing a high potential for precipitation processes during annealing at 220°÷470°C. The cold deformation was found to contribute the electrical resistivity intensively at the beginning of deformation (in the range up to ∼20%), and it was not influenced by the chemical composition of tested alloys. The resistivity variations with the cold deformation were fitted by power-law equations.     

Effects of Cr,Mn, Si,Cu and Zr on microstructure and mechanical properties of high carbon Fe–16Al alloy

Abstract

Effects of alloying elements Cr, Mn, Si, Cu and Zr on the microstructure and mechanical properties of Fe₃Al (Fe–16Al) based alloy containing ～0·5 wt-%C have been investigated. Six alloys were prepared by a combination of air induction melting with flux cover and electroslag refining (ESR). ESR ingots were hot forged and hot rolled at 1373 K and were further characterised with respect to microstructure and mechanical properties. The base alloy and the alloys containing Cr, Mn, Si and Cu exhibit a two phase microstructure of Fe₃AlC_0·5 precipitates in Fe₃Al matrix whereas the alloy containing Zr exhibits a three phase microstructure, the additional phase being Zr rich carbide precipitates. Cr and Mn have high solubility in Fe₃AlC_0·5 precipitates as compared to Fe₃Al matrix whereas Cu and Si have very high solubility in Fe₃Al matrix compared to Fe₃AlC_0·5 precipitate and Zr has very low solubility in both Fe₃Al matrix and Fe₃AlC_0·5 precipitate. No significant improvement in room and high temperature (at 873 K) strengths was observed by addition of these alloying elements. Furthermore, it was observed that addition of these alloying elements has resulted in poor room and high temperature ductility. Addition of Cr, Mn, Si and Cu has resulted in marginal improvement in creep life, whereas Zr improved the creep life significantly from 22·3 to 117 h.     

Effect of some alloying elements on boiling point of magnesium

Abstract

The evaporation capacity of alloys differs with temperature, and this is the basis of a new experimental method to measure the boiling points of various kinds of alloys. In the present work, the effects of Al, Zn, Mn and La additions on the boiling point of magnesium have been studied. It is shown that various elemental additions and their varying contents in magnesium alloys have different influences on the boiling point of the alloys. Among these additions, Zn affected the boiling point of magnesium alloys most obviously, followed by Mn, Al and La. The boiling point of Mg–6 wt-%Zn alloy was the highest in the present study, up to 1715 K.