Mechanical properties of Fe-Co soft magnets

The tensile behavior of two magnetically soft alloys, Fe-49Co-2V and Fe-27Co, has been characterized as a function of testing temperature, grain size, and degree of long-range order. Several trends in the yield strength of the two alloys have been noted and possible mechanisms for their occurrence discussed. Ordering is found to markedly lower the yield strength of the Fe-49Co-2V. Both alloys exhibit three distinct regions in their yield strength vs. temperature curves. At lower and higher temperatures, i.e. regions I and III, the yield strength shows the normal drop with increasing temperature. In the intermediate temperature range (region II), however, Fe-49Co-2V with a B2 ordered structure demonstrates an anomalous strengthening with increasing temperature while the yield strength remains constant in the disordered Fe-27Co. Both alloys exhibit a Hall-Petch type relationship in their yield strength as a function of grain size and show a decrease in the strain hardening coefficient with increasing grain size.     

微量Cu和形变热处理对Al-Fe合金性能的影响

观察Al-Fe合金的显微组织并测量其力学性能和导电性能,研究了Cu元素和形变热处理对其性能的影响。结果表明：在铸态Al-Fe-Cu合金组织中,Cu元素在基体内均匀分布,而Fe元素在晶界处偏析;挤压态的Al-0.7Fe-0.2Cu合金其性能最优：导电率为59.90%IACS,抗拉强度为108 MPa,硬度为31.2HV;随着退火温度的提高Al-0.7Fe-0.2Cu合金的抗拉强度急剧降低,在400℃退火时其抗拉强度最低(100 MPa),伸长率最高(31.3%);在250℃退火时导电率出现峰值(62.61%IACS)。在退火Al-0.7Cu-0.2Cu合金中有许多细小针状的θ(Al₂Cu)相析出,并与位错交互缠结。随着退火温度的提高合金中的位错密度降低,晶粒细化。     

Near equiatomic FeCo alloys: Constitution, mechanical and magnetic properties

Alloys based on the near-equiatomic FeCo offer exceptional magnetic properties. The equiatomic alloy was ‘invented’ in 1929, it offers a saturation hardly lower than that of the maximum obtained for Fe-0.35Co, with higher permeability and a lower coercivity than the latter. However, this alloy remained without industrial application, mainly because of its extreme brittleness. Only with the addition of a third element did it become possible to impart sufficient ductility for cold-rolling, and develop applications as laminated products. The addition of 2 wt% vanadium (1932) led to the ubiquitous FeCo-2V, or Permendur. It not only imparts, given appropriate heat-treatments, sufficient ductility, but also increases significantly the resistivity of the alloy while having little impact on the saturation.From a scientific point of view, the FeCo alloys, with their B2 structure below 730 °C, fall in the interesting category of ordered compounds. The ordering reaction has significant influence on the mechanical and magnetic properties and has therefore prompted a number of investigations. Not surprisingly, the vast majority of the work published to date concerns the FeCo-2V or its variants, rather than the binary alloy or other ternary systems. Recently though, alternative compositions, or improvement on the basic FeCo-2V have been put forward.This review attempts to summarise the current knowledge about the constitution, mechanical and magnetic properties of these alloys, focussing on the general properties of bulk FeCo and FeCo-X alloys (developed for applications such as rotor or stator laminations in motors). Recent development of nanocomposite and nanocrystalline materials such as HITPERM are not considered. A review of this developments is available in [McHenry ME, Willard MA, Laughlin DE. Amorphous and nanocrystalline materials for applications as soft magnets. Prog Mater Sci 1999;44:291-433]. An overview is given of work undertaken to date on various FeCo-X ternary system, with emphasis on the influence of these ternary additions on microstructure and characteristics of the phase diagram. The problem of the kinetics of ordering is given particular attention. Magnetic and mechanical properties are then discussed with emphasis on the relationship between microstructure and properties, and the main quantitative theories put forward are assessed again data gathered from the literature. It is shown that, while some points are clearly understood, a number of question remains in different areas which are outlined.     

High-temperature strength-coercivity balance in a FeCo-based soft magnetic alloy via magnetic nanoprecipitates

Precipitation strengthening is an effective approach to enhance the strength of soft magnetic alloys for applications at high temperatures,while inevitably results in deterioration in coercivity due to the pinning effect on the domain wall movement.Here,we realize a good combination of high-temperature strength and ductility (ultimate tensile strength of 564 MPa and elongation of ～ 20 ％,respectively) as well as low coercivity (6.97 Oe) of FeCo-2V-0.3Cr-0.2Mo soft magnetic alloy through introducing high-density magnetic nanoprecipitates.The magnetic nanoprecipitates are characterized by FeCo-based phase with disordered body-centered cubic structure,whichenables the alloy to have a low coercivity.In addition,these nanoprecipitates can impede the dislocation motion and suppress the brittle fracture,which lead to a high tensile strength and ductility.This work provides a guideline to enhance strength and ductility while maintaining low coercivity in soft magnetic alloys via magnetic nanoprecipitates.     

Residual stress estimation of a silicon carbide-Kovar joint

Residual stress of silicon carbide and Kovar is calculated using the elasto-plastic method and its validity is checked by the four-point bending test. Silicon carbide and Kovar (Fe-27% Ni-7% Co) are diffusion bonded using Al-10% Si alloy clad on a pure aluminium sheet at 883 K and 4.9 MPa under a vacuum condition. The non-linear structure analysis program (ADINA) is used for the stress estimation. It is found by the calculation that the maximum tensile stress, about 170 MPa, is generated in the silicon carbide close to the interlayer. In the bending test, the fracture of the joint is found to occur from the point where the maximum calculated tensile stress is generated, and the bending strength of the joint is 113 MPa. It becomes clear that the calculated stress and the measured strength of the joint is nearly equal to the strength of the silicon carbide itself (280 MPa). Therefore, it can be concluded that the stress estimation in this method indicates a good approximation of the practical residual stress of the joint.     

Texture and magnetic properties of rapidly quenched Fe-6.5wt%Si ribbon

Rapidly quenched Fe-6.5wt%Si alloy has been fabricated as 2.5 cm wide ribbon using the planar flow casting process. The magnetic properties have been investigated for various heat treatment conditions. The relationship between core loss and exciting power vis-avis texture and microstructure of the as-cast and annealed ribbons is discussed. The best magnetic properties obtained-a core loss of 0.46 W/kg and an exciting power of 0.62 VA/kg at B = 1.0 T and f= 60 Hz-are considerably better than those for commercial nonoriented Fe- 3wt%Si steel, but inferior to those for commercial amorphous metallic glasses. The magnetic properties are isotropic in the plane of the ribbon. which makes this material attractive for applications in rotating devices.     

室温应变速率及Al含量对FeAl合金拉伸性能的影响

研究了初始应变速率在１．３９×１０＾４￣６．９５×１０＾－１ｓ＾－１范围内Ｆｅ－４０Ａｌ的室温拉伸性能。结果发现，应变速率对ＦｅＡｌ合金室温下的断裂延伸率屈服强度和抗拉强度均有不同程度的影响，其中对断裂延伸率的影响最为显著。应变速率对ＦｅＡｌ合金力学性能的影响程度还与Ａｌ含量有关，Ｆｅ－３６．５Ａｌ较Ｆｅ－４０Ａｌ合金受应变速率的影响更大，研究结果还表明，Ａｌ含量还影响着ＦｅＡｌ合金拉伸断口中穿晶     

Microstructure, mechanical property and chemical property in Ni3Al-Ni3Ti-Ni3Nb-based multi-intermetallic alloys

Microstructure, high-temperature compressive and tensile deformation, and corrosion property of multi-phase alloys based on Ni₃Al-Ni₃Ti-Ni₃Nb pseudo-ternary alloy system were investigated. The microstructures of these alloys were largely dependent on alloy composition but independent of annealing temperature. Alloys composed of multi-phase microstructures of L1₂, D0₂₄ and D0_a showed substantially enhanced compressive yield stress as well as a certain amount of compressive plasticity at whole temperature, while they did not show reasonable tensile elongation at whole temperature. Also, alloys composed of lamellar-like multi-phase microstructures are effective in enhancing compressive yield stress particularly at high temperature. Multi-phase alloys with low Nb contents have good corrosion resistance, especially in high concentration of sulfuric acid.     

Measurement of the stress field created within the resin between fibres in a composite material during cooling from the cure temperature

In a long uniaxial glass fibre/epoxy resin composite that is constrained by a rigid outer shell not to change its overall external dimensions, the transverse components of principal stress generated during cooling from the temperature of cure have been measured at various distances from the specimen ends. The radial (compressive) and hoop (tensile) components of stress in the resin between four fibres whose axes define the edge of a prism with square section are in excess of 6 and 100 MPa, respectively. In an identical specimen, 4 days of exposure to distilled water at 80° C was found to give rise to a tensile hoop stress of magnitude sufficient to cause fracture of the rigid outer shell.     

Effect of Surface Modification on Room Temperature Tensile Properties for Fe-18A1 and Fe-18AI-5Cr Alloys

The influence of surface modifications on the room-temperature ductility of the Fe-18A1 and Fe-18Al-5Cr alloys was investigated. A variety of surface modification techniques including electroplating, magnetron sputtering and pack treatment were applied to the alloys to produce various protective coatings. From the results of tensile tests in air (70% humidity) at room temperature for the specimens in different surface conditions, several observations can be summarized.

1. The nickel-coating layer by using either electroplating or sputtering deposition had a limited effect on the ductility of alloys.

2. The chromium-coating layer by the electroplating technique had a negative effect on the ductility of alloys,

3. The specimen of Fe-18A1 alloy conducted by packing treatment at 1000°C for 8 hours had the highest elongation (19.6%) among those specimens studied.

The significant improvement in the tensile ductility of Fe-18A1 and Fe-18Al-5Cr alloys by pack treatment are related to the forming of aluminum oxide layer and Al-depleted alloy layer on the specimen surface.     

Nickel-free austenitic steels for cryogenic applications: The Fe-23% Mn-5% Al-0.2% C alloys

A study has been made of the influence of carbon and aluminium additions on the mechanical properties under uniaxial tensile loading and by Charpy V notch impact tests at room temperature and ?196°C on the Fe-24 % Mn alloys. It is concluded that the Fe-24 % Mn-5 % Al-0.2 % C appears as a new nickel-free iron-based alloy which is particularly interesting for cryogenic applications. In these alloys, both additions of carbon and aluminium contribute to the stability of the austenitic phase by suppressing the γ → ? martensitic transformation of the binary Fe-24 % Mn and to the solution hardening of the manganese-rich austenitic alloy.     

Effect of thermomechanical treatment on the properties of Fe-11Al and Fe-14Al alloys

Fe-Al alloys have the potential to be relatively inexpensive soft magnetic materials if their formability could be improved. An investigation has been made on the effect of thermomechanical treatment on the properties of Fe-11 wt%Al and Fe-14 wt%Al alloys (designated Fe-11Al and Fe-14Al respectively). For the former the room temperature mechanical properties were found to be determined principally by the recrystallised grain size. A good combination of properties for Fe-11Al, i.e. high strength and ductility, was obtained when the grain size was less than about 100 m. The small grain size was produced by warm rolling at 600°C followed by 1 hour annealing at 600–700°C. On the other hand hot rolling followed by annealing resulted in large grain size, hence rendered the alloy brittle. The cold formability also exhibited a grain size dependence, with the Fe-11Al alloy with a fine recrystallised grain size having good cold rollability. In contrast Fe-14Al was brittle irrespective of the treatment given; ductility of less than 1% was observed in all cases and the cold rollability was limited. Ordering was not seen to be a factor affecting the observed mechanical properties and rollability of either alloy as all the thermomechanical treatments, other than an ordering treatment of 500 hours at 400°C, resulted in a disordered structure. The stress required to work these alloys at elevated temperatures were estimated from compression tests and it is apparent that for Fe-11Al the stress is greatly reduced (50%) from the room temperature value at 600°C and that at 750°C both alloys required a similar stress which was about 15% of the room temperature value. The magnetic properties of Fe-11Al compared favourably with Fe-14Al; the former has a higher saturation induction, a similar coercive force but a lower permeability than Fe-14Al.     

Effect of 1.5 wt% tin addition on the properties of AZ31 magnesium alloy

In this paper, 1.5 wt%Sn was added to the AZ31 magnesium alloy aiming at improving the mechanical properties by using a low cost alloying element. Both alloys were prepared in the cast/heat treated (HT), rolled at 350 °C, rolled/heat treated at 400 °C and extruded at 350 °C. The results indicate that with addition of tin an improvement was obtained in both tensile strength and ductility of the AZ31 alloy in the cast/heat treated and in the extruded conditions. The yield and ultimate tensile strengths reached 98 MPa and 224 MPa respectively with 14 % elongation in the cast/heat treated condition while in the extruded condition these values were 212 MPa and 286 MPa with 20 % elongation. The tensile strength was even higher after rolling reaching 315 MPa for AZ31 with tin addition; however, as the material temperature during the last passes has decreased to relatively low values, the % elongation decreased to 1 %. After heat treatment at 400 °C for 2 hours the % elongation was restored and reached 12 %; this was accompanied by a decrease in tensile strength which reached 276 MPa. The results are discussed in relation to the microstructure evolution including grain size, phase identification, and volume fraction of phases.     

Microstructure and mechanical properties of RSP/M Al-Fe-V-Si and Al-Fe-Ce alloys

Two aluminium alloys with nominal compositions of Al-8Fe-4Ce and Al-8Fe-1V-2Si (all compositions in wt%) were rapidly solidified by ultrasonic gas atomization. The atomized powders with an average particle size (d₅₀) of 30 m were vacuum hot pressed and subsequently hot extruded. The P/M extrusion exhibited similar microstructure and elevated temperature tensile properties. The tensile and stress rupture samples of both the alloys exhibited ductile dimple failure. However, the Al-Fe-V-Si extrusion samples exhibited significantly better creep and stress rupture properties. The Al-Fe-Ce alloy was found to be more susceptible to cavitation at elevated temperatures which resulted in poor stress rupture properties.     

On the deformation behavior of single crystalline Fe---Al

Compression tests were performed on two single crystalline alloys with the B2 (CsCl) crystal structure, FeAl and Fe-45Al. Testing was done in air and test temperatures ranged from room temperature to 1273 K. Results show that limited {123} slip was produced in FeAl at low temperatures followed by the addition of {110} slip. {211} slip was produced in the Fe-45Al alloy up to 1073 K after which {110} slip was also observed. The flow stress vs. temperature curve of FeAl showed high compressive stresses up to 973 K followed by a large decrease in stress with increasing temperature. The flow stress versus temperature curve for Fe-45Al showed a very weak temperature dependence up to 973 K followed by a gradual decrease in stress with increasing temperature. Below 973 K, the flow stress values of Fe-45Al were calculated to be 50 to 60% of the values of FeAl.     

冷轧对Al_(10)Cu_(25)Co_(20)Fe_(20)Ni_(25)高熵合金组织结构及力学性能的影响

对铸态Al10Cu25Co20Fe20Ni25高熵合金进行冷轧处理后进行室温拉伸测试,并利用X射线衍射仪(XRD)和扫描电镜(SEM)分别对其相结构、微观组织形貌及拉伸断口进行分析。结果表明:经冷轧工艺处理后,Al10Cu25Co20Fe20Ni25高熵合金硬度最大为285HV,较轧制前提高了51.6%;在变形量为40%时,抗拉强度达到最大值,为638MPa,是铸态合金的2.7倍。拉伸断口分析表明,铸态合金的断裂模式为树枝晶沿晶断裂和韧窝型延性断裂,而冷轧态合金主要为韧窝型延性断裂模式。     

Low‐cycle fatigue behavior of a newly developed cast aluminum alloy for automotive applications

The drive for increasing fuel efficiency and decreasing anthropogenic greenhouse effect via lightweighting leads to the development of several new Al alloys. The effect of Mn and Fe addition on the microstructure of Al‐Mg‐Si alloy in as‐cast condition was investigated. The mechanical properties including strain‐controlled low‐cycle fatigue characteristics were evaluated. The microstructure of the as‐cast alloy consisted of globular primary α‐Al phase and characteristic Mg₂Si‐containing eutectic structure, along with Al₈(Fe,Mn)₂Si particles randomly distributed in the matrix. Relative to several commercial alloys including A319 cast alloy, the present alloy exhibited superior tensile properties without trade‐off in elongation and improved fatigue life due to the unique microstructure with fine grains and random textures. The as‐cast alloy possessed yield stress, ultimate tensile strength, and elongation of about 185 MPa, 304 MPa, and 6.3%, respectively. The stress‐strain hysteresis loops were symmetrical and approximately followed Masing behavior. The fatigue life of the as‐cast alloy was attained to be higher than that of several commercial cast and wrought Al alloys. Cyclic hardening occurred at higher strain amplitudes from 0.3% to 0.8%, while cyclic stabilization sustained at lower strain amplitudes of ≤0.2%. Examination of fractured surfaces revealed that fatigue crack initiated from the specimen surface/near‐surface, and crack propagation occurred mainly in the formation of fatigue striations.     

Hot tensile and fatigue behaviour of zinc–aluminum alloys produced by gravity and squeeze casting

The tensile and fatigue properties of zinc–aluminum alloys (ZA-8, ZA-12 and ZA-27) in squeeze and gravity cast forms have been investigated. Tensile tests were conducted at ambient and elevated temperatures up to 150 °C. At low temperatures, the ultimate tensile strength and yielding strength of the squeeze cast alloys have been found to be superior those of the gravity-cast alloys, as the temperature increased they decreased. In the same way, Brinell hardness of the squeeze cast alloys were obtained at higher values than gravity castings. The fatigue tests were performed at a constant speed of 400 rev/min and under a number of stress levels ranging from 100 to 150 MPa. The fatigue behaviour results of the ZA alloys were similar to obtained from the tensile testing. The squeeze cast alloys exhibited good fatigue resistance in proportion to the gravity castings. Metallography examinations showed that the microstructure of the castings differed according to the method of casting used. It was considered that the mechanical properties of the alloys were affected from these micro-structural changes.     

Phase transition and mechanical properties of constraint-aged Ni–Mn–Ga–Ti magnetic shape memory alloy

Ni–Mn–Ga Heusler-type ferromagnetic shape memory alloys are attractive materials for micro-actuator, but the relatively poor ductility and low strength of Ni–Mn–Ga alloys have triggered a great deal of interest. In this study, we attempt to introduce some ductile second phase in the alloy by partially substituting Ti for Ga and constraint aging treatment. The results show that the martensitic transformation temperature first decreases and then increases slightly with the increasing of constraint-aging temperature, which can be attributed to the decrease of Ni content in the matrix and strengthening effect of the second particles. It is found that the amount of the Ni-rich precipitates by constraint-aged samples is more and the size of the second phase particle is smaller than that of the free-aged samples. The compressive stress and ductility can be significantly improved by the constraint-aging treatment, and the maximum compressive stress for constraint-aging alloy is about 1400 MPa, which is the highest value up to date compared with the 400 MPa in solution-treated Ni–Mn–Ga–Ti alloy and about 900 MPa in Ni–Mn–Ga–Ti alloy free-aged at 1073 K for 3 h. Scanning electron microscopy observations of fracture surfaces confirm that the Ni-rich second phase play a key role in improving the compression stress and ductility of Ni–Mn–Ga–Ti alloy.     

固溶体Mg-5Al-xGd合金的制备及其压缩性能EI北大核心

利用Gd(0.00%,0.25%,0.50%,0.75%,1.00%,质量分数,下同)元素和凝固压力(3 GPa)调控Mg-5Al合金凝固组织结构,对合金样品进行压缩测试,并研究组织结构与室温压缩性能相关性。结果表明:常压石墨型铸造下,仅Mg-5Al-0.75Gd合金获得了晶界无共晶相生成、粒状Al2Gd相弥散分布在基体上、晶粒平均尺寸约为85μm的固溶体组织,其抗压强度和最大压缩应变分别为379 MPa和33.46%,高于存在晶间第二相的合金。3 GPa高压下,Gd含量≤0.25%合金的凝固组织为单一固溶体,Gd含量≥0.50%合金的晶界(枝晶间)有共晶Al_(2)Gd相生成。固溶体Mg-5Al-0.25Gd合金的平均晶粒尺寸是74μm,抗压强度是402 MPa,最大压缩应变是33.61%。Mg-5Al-0.75Gd合金的平均晶粒尺寸是38μm,抗压强度和最大压缩应变分别是341 MPa和25.12%,其性能低于Mg-5Al-0.25Gd合金。可见,晶间Al,Gd元素的存在形式是影响铸造Mg-Al合金力学性能的重要因素。