粉末冶金法制备WC-Ni3Al复合材料的组织与性能

在WC粉末中直接添加Ni、Al元素粉末,通过在液相烧结过程中反应合成Ni3Al来制备WC-Ni3Al复合材料,对该材料进行组织结构观察及力学性能测定,分析铝含量对合金致密化和镍铝相形成种类的影响,并对材料的抗氧化性能进行测试。结果表明,制备的WC-Ni3Al复合材料具有圆钝的WC晶粒形貌,粘结相中除Ni3Al相外还有少量的NiAl和Ni相;铝含量对WC-Ni3Al材料致密度的影响主要与高熔点的NiAl的形成量有关。与普通WC-15Ni硬质合金的抗弯强度(1 900 MPa)和硬度(82.6 HRA)相比,WC-15Ni3Al复合材料具有低的室温抗弯强度和高的硬度,分别为1 170 MPa和86.5 HRA。随Ni3Al含量(质量分数)从15%增加到30%,WC-30Ni3Al复合材料的室温抗弯强度增加,而硬度降低,分别为1 660 MPa和81.7 HRA,其高温抗氧化性能比WC-30(Co-Ni-Cr)硬质合金提高1个数量级。     

The fracture resistance of directionally solidified dual-phase NiAl reinforced with refractory metals

The fracture resistance of two directionally-solidified, NiAl refractory metal systems has been measured and analyzed. One system, NiAl/Mo, has a microstructure consisting of Mo rods. The second system, NiAl/Cr(Mo), has a layered microstructure. Both materials are found to have an appreciably higher initiation toughness than NiAl, followed by a rising resistance, with the layered microstructure giving the superior properties. The results have been rationalized by available models based on the following three mechanisms: crack trapping, crack renucleation and ductile phase bridging.     

Influences of Yttrium on Microstructure and Mechanical Properties of NiAl-28Cr-5.5Mo-0.5Hf Alloy

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Microstructures and mechanical behavior of NiAl-Mo and NiAl-Mo-Ti two-phase alloys

The phase relationship in the NiAI-Mo system is characterized by a eutectic equilibrium between binary NiAl and the terminal (Mo) solid solution, thereby offering the potential for development of ductile-phase-toughened composites. A study was conducted to evaluate the effect of varying volume fraction of the (Mo) phase on the microstructure, bend strength, and ambient temperature fracture behavior of selected NiAI-Mo two-phase alloys. Above room temperature, the NiAI-Mo alloys showed an increase in bend strength compared to monolithic NiAl, with reasonable strength retention up to ≈800 °C. The results demonstrated moderate improvements in toughness in the NiAI-Mo alloys in comparison to monolithic NiAl. A further enhancement in toughness was realized through hot working. Fractography studies showed evidence for substantial decohesion between the (Mo) phase and the NiAl matrix, thereby suggesting the presence of a weak interface. This weak interface between the (Mo) phase and the NiAl matrix, in conjunction with modulus mismatch stresses, causes the crack to deflect from the (Mo) rein-forcement and propagate preferentially along the (Mo)/NiAl interface. These attributes limit the potential for significant ductile-phase toughening in the NiAI-Mo system. An addition of 0.2 at. pct Ti resulted in a marked improvement in the room-temperature fracture toughness of NiAI-Mo. Fractography observations show some evidence for (Mo)/NiAl interface strengthening with the Ti addition.     

Joining of NiAl to iron-based alloys by reactive casting

Nickel monoaluminide, NiAl, is exothermically synthesized from elemental liquids of aluminum and nickel and is simultaneously joined to iron-based alloys, such as carbon steels and stainless steels, by the reactive casting method, which is based on the pouring of the elemental liquids onto the base material. The exothermic reaction between the aluminum and nickel liquids produces extremely superheated NiAl liquid. Heat of the NiAl liquid is transferred to the base material, and the contact surface is melted to a depth depending on both the preheating temperature of the base material and the thickness of the NiAl produced. After solification on the base material, NiAl is strongly joined to the base material, showing a joint strength exceeding the inherent strength of NiAl. The high joint strength is attributed to a very fine, rodlike eutectic structure at the joint interface that consists of a mixture of β-NiAl and γ-iron with an interrod spacing of approximately 100 nm.     

Correlation of deformation mechanisms with the tensile and compressive behavior of NiAl and NiAl(Zr) intermetallic alloys

To identify the mechanisms controlling strength and ductility in powder-extruded NiAl and NiAl + 0.05 at. pct Zr, tensile and compressive testing was performed from 300 to 1300 K for several grain sizes. Grain size refinement significantly increased yield stress in both alloys and, in some cases, slightly lowered the ductile-to-brittle transition temperature (DBTT), although no room-temperature tensile ductility was observed even in the finest grain size specimens. The small Zr addition increased the DBTT and changed the low-temperature fracture mode from intergranular in NiAl to a combination of intergranular and transgranular in the Zr-doped alloy. Scanning electron microscopy (SEM) of compression specimens deformed at room temperature revealed the presence of grain-boundary cracks in both alloys. These cracks were due to the incompatibility of strain in the poly crystalline material, owing to the lack of five independent slip systems. The tendency to form grain-boundary cracks, in addition to the low fracture stress of these alloys, contributed to the lack of tensile ductility at low temperatures. The operative slip system, both below and above the DBTT, was {110} 〈001〉 for both alloys. The change from brittle to ductile behavior with increasing temperatures was associated with the onset of diffusional processes.     

微掺镧钼丝组织和性能

系统地研究了纯钼丝、微掺镧钼丝在不同温度下退火后的组织和性能。结果表明，微掺镧显著地改善了钼丝的强韧性能，提高了钼丝的室温强度和再结晶温度，改善了丝材再结晶后的室温脆性。微掺镧钼丝综合性能明显高于纯钼丝。     

微量硼和铌对铸造Ni50Al20Fe30合金组织及性能的影响

研究了微量硼和2％Nb对铸造Ni50Al20Fe30合金组织及性能的影响。结果表明：微量硼的加入可以改善Ni50Al20Fe30合金的强度与塑性,最佳硼含量为0．02％－0．05％;此外,微量硼的加入影响该合金的共晶区,从而明显改变合金的微观组织形态。在硼含量为0．02％时,该合金主要处于β相（NiAl)与γ相的共晶区,这对合金的室温塑性极为有利。添加2％Nb可明显提高合金的压缩屈服强度并改善塑性。在室温、650℃和10000170,该合金的压缩屈服强度分别提高30％,59％和36％。     

Fatigue Behavior of Dual‐Phase and TWIP Steels for Lightweight Automotive Structures

Car bodies are increasingly made with high‐strength steels, for both lightweighting and safety purposes. Steel sheets, made by continuous casting, hot rolling, cold rolling, and continuous heat treating, are used to deep draw the car body parts, which are then joined by resistance spot welding (RSW). Two high‐strength automotive steels, with similar tensile strength, are studied here. The low alloy, dual‐phase steel consist of ferrite and martensite, obtained by an intercritical heat treatment, followed by fast cooling. The innovative, high‐Mn TWIP steel exhibits a promising combination of strength and toughness, arising from the austenitic structure, strengthened by C, and from the twinning induced plasticity effect. Tensile specimens are fatigue tested at room temperature with zero load ratio, both in the as‐fabricated (unnotched) condition and after the RSW of an homologous sheet square. Moreover, pre‐cracked compact tension specimens are tested with load ratio 0.1 to determine the fatigue crack growth behavior. These results are completed with crystallographic, microstructural, tensile, and fractographic examinations, and the influence of the microstructure and of the welding process is discussed.     

The role of deformation twinning on mechanical properties of an austenitic Fe30Mn1.2Al0.3C alloy

An austenitic Fe30Mn1.2Al0.3C alloy has been investigated under tensile and total-strain controlled fatigue tests between room temperature and 77K. The alloy exhibits an elongation peak between room temperature and 77K. It was found that tensile elongation is not controlled by the total amount of deformation twinning, but rather the rate and temperature sensitivity of deformation twin formation. Total-strain-controlled fatigue tests show that the fatigue resistance of the Fe30Mn1.2Al0.3C alloy at 77K is superior to that at room temperature in the 10²–10⁴ cycles fatigue life range, although the monotonic tensile elongation at 77K is lower than that at room temperature. The enhancement of fatigue resistance at 77K is due both to an increased fatigue ductility coefficient, because of strain-induced deformation twins, and to increased strength. Increased formation of deformation twins during the fatigue test is responsible for the increased fatigue resistance at 77K.     

Properties and application of TRIP‐steel in sheet metal forming

A further development of dual‐phase‐steels are represented by TRIP (transformation induced plasticity) ‐steels. TRIP‐steels contain austenite, which is metastable at room temperature. It transforms to martensite during straining (TRIP effect). This process improves the strength‐ductility balance of these steels. Two types of TRIP‐steels, low alloyed (L‐TRIP) and high alloyed (H‐TRIP), can be applied in sheet forming processes and exhibit different forming characteristics. Basing on results of uniaxial tensile tests and the evaluation of Young's modulus the forming limits in deep drawing processes and the component properties of deep drawn parts are discussed. The Young's modulus decreases significantly with increasing pre‐strain, especially demonstrated for the L‐TRIP material TRIP700. Forming limit curves determined at different forming temperatures indicate its influence on the forming limits. Martensite transformation is suppressed at a temperature of approximately T = 200 °C and therefore the major strain ?₁ decreases significantly. For the investigated stainless steel AISI304 (H‐TRIP) different lubricant types in comparison to chlorinated paraffins have been tested. Lubricants consisting of sulphur additives led to good forming conditions in forming processes, even better than lubricants based on chlorinated paraffins. The evaluation of component properties, compared between L‐TRIP and H‐TRIP, was done based on the analysis of springback and dent resistance. The L‐TRIP material TRIP700 shows higher springback angles than AISI304 resulting from higher yield strength and decreased Young's modulus, resulting from the forming process. The dent resistance of TRIP‐steel was exemplarily demonstrated for AISI304. Uniaxial pre‐strained sheet specimen were analysed to show the dent resistance depending on dent depth. During elastic denting pre‐strain has no influence on dent resistance. Further increasing dent depth lead to increased dent forces for pre‐strained specimens.     

Formation of voids and dislocation loops in near-stoichiometric nial by aging at 700° to 900°c,and some effects on alloy properties

Dislocation loops and voids form spontaneously in stoichiometric NiAl annealed between 700° to 900°C. The former probably are formed by a punching mechanism from impurity particles, and the latter are frequently seen to have nucleated on particles. However, it is possible that both loops and voids are nucleated by vacancy/impurity complexes. Some of the loops act as dislocation sources during plastic deformation so that, for example, NiAl annealed at 700° to 900°C is softer and has greater ductility at room temperature, or has poorer creep resistance at higher temperatures, than material annealed at 1300°C. It is probable that small precipitate particles, possibly carbides and/or aluminum oxide form at 700° to 900°C but are in solution at higher temperatures. Their effect on mechanical properties is a form of precipitation softening.     

Dislocation substructure in NiAl single crystals cyclically deformed at ambient temperature

Dislocation structures have been characterised in cyclically deformed NiAl single crystals tested at room temperature. The primary slip system <001>{110} was found to be in operation for the <112> ‘soft’ orientation. The dislocation structure was found to have a high density of dipoles and point defect clusters. Dislocation cross grids that accommodate the misfit between PSBs (persistent slip bands) and the matrix were observed. Possible cyclic hardening mechanisms at room temperature are discussed. The density of the dipoles was not uniform and was found to be modulated on the slip plane, unlike Ni₃Al which shows a homogeneous distribution. Computer simulation of the microstructure has been carried out, based on the mechanism of dipole diffusion in a stress gradient.     

Elevated temperature compressive properties of Zr-modified NiAl

Small Zr additions are known to substantially affect the deformation behavior and strength of po-lycrystalline NiAl, yet little information is currently available regarding the high-temperature prop-erties of such alloys. Utilizing prealloyed powder technology, a series of four NiAl alloys have been produced containing from 0.05 to 0.7 at. pct Zr. The creep behavior of these alloys was characterized in compression between 1000 and 1400 K at strain rates ranging from ∼0.1 to 10^-9 s^-1. All the Zr-modified alloys were significantly stronger than binary NiAl under lower temperature and faster strain-rate conditions; however, the single-phase materials (Zr ≤ 0.1 at. pct) and binary NiAl had similar strengths at high temperatures and slow strain rates. The two-phase NiAl-Ni₂AlZr alloys containing 0.3 and 0.7 at. pct Zr had nearly identical strengths. While the two-phase alloys were stronger than the single-phase materials at all test conditions, the degree of microstructural damage in the two-phase alloys due to internal oxidation during testing appeared to increase with Zr level. Balancing the poor oxidation behavior with the consistent strength advantage of the two-phase alloys, it is concluded that optimum elevated-temperature properties could be obtained in Heusler-strength-ened NiAl containing between 0.1 and 0.3 at. pct Zr.     

平整对罩式退火生产BH钢板力学性能和自然时效性能的影响

研究了平整对罩式退火生产的BH钢板力学性能和自然时效性能的影响。结果表明，平整对BH钢的BH性能有显著影响，平整延伸率在1．0％～2．0％之间时BH值有最大值；平整使得BH钢的屈服强度先下降而后上升，屈服强度最小时的平整延伸率消除了钢板单向拉伸时的屈服点延伸现象；足够的平整延伸率是BH钢抗自然时效性能的有效保证。实验结果在工业生产中得到了应用。     

Preliminary studies on NiAl/Nb2Be17 reaction and effectiveness of BeO as an interfacial reaction barrier

Alloys based on the ordered B2 NiAl phase are being considered as potential high-temperature structural materials. One drawback for this material is its lack of high-temperature strength,[1] which can be overcome by reinforcing the alloy with high-strength fibers. Like any other composite system, a suitable reinforcement material must have a matching coefficient of thermal expansion (CTE) with the matrix in addition to high-temperature strength and be chemically compatible with the matrix. Although there are many high-melting ceramic materials which are thermodynamicalry stable in the NiAl matrix, [2] the high CTE of NiAl,[3] 16 X 10⁻⁶ K⁻¹ at 1200 K, makes it difficult to find a suitable ceramic reinforcement material with a matching CTE. Thus, there is a need to develop high CTE fibers for the NiAl matrix. One group of materials with matching CTE[3] to NiAl are the Be-rich intermetallic compounds called beryllides (CTEs in the range of 16 to 18 × 10⁻⁶ K₋₁ at 1200 K) of formula M₂Be₁₇, M₂Be₁₃, or M₂Be₁₂ (where M = Ta, Nb, Ti, Zr, Hf, or Y). Matching CTEs with the NiAl matrix along with their good high-temperature strength[4] and low densities[4] make Be-rich intermetallic compounds attractive as candidate reinforcement materials for the NiAl matrix.     

Development of New Wear-Resistant Surface Coating at Elevated Temperature

Metal matrix composites containing a high vol-ume fraction of carbide particles are frequently usedas wear-resistant materials[1 -4]. For elevated tem-perature service in air ,the oxidation resistance andthe hot hardness of hard particle are the most i mpor-tant factors .In metal carbides ,tungsten carbide andchromiumcarbide can act as hard particles in metalmatrix in order to increase their hot hardness andthe ability of wetting metal matrix. Compared withtungsten carbide ,chromiumcarbide is …     

NiAl金属间化合物的研究进展

对NiAl金属间化合物的国内外研究现状如改善NiAl合金力学性能和高温抗氧化性能等所 采用的合金化、制备多相合金、制备复合材料、定向凝固、机械合金化、热压及热等静压、燃烧合成、 微晶涂层等工艺以及NiAl合金的超塑性行为进行了系统综述,着重介绍并论述了合金化及定向 凝固等工艺。此外,还介绍了NiAl合金的固溶强化磁行为。     

快速凝固粉末冶金Al－Si－Cu－Mg合金的组织和性能

本文详细论述了快速凝固Ａｌ－１８．６Ｓｉ－４．３４Ｃｕ－０．６６Ｍｇ合金的制备工艺，研究了这种高硅铝合金的力学性能与组织结构的关系。实验结果表明：快速凝固Ａｌ－Ｓｉ－Ｃｕ－Ｍｇ合金的强度、硬度和塑性明显提高，固溶时效处理后的室温拉伸强度高达４３０ＭＰａ。随着试验温度的升高，其拉伸强度下降，但在２００℃时。бｂ能保持在３７０ＭＰａ。Ａｌ－Ｓｉ合金这样优良的高温热稳定性是一般常规高强铝合金难以达到的。     

成品退火工艺对罐箱用316L奥氏体不锈钢组织及性能影响研究

通过对罐箱用超低碳奥氏体不锈钢316L的热处理工艺试验,研究了不同温度和保温时间对材料组织、常温和高温（130℃）力学性能及耐晶间腐蚀性能的影响规律。结果表明,随着温度的提高和保温时间的延长,材料的晶粒变大,常温和高温强度指标得到提高,而塑性减小。耐晶间腐蚀性能在本实验的各种参数条件下均表现合格,说明碳已经完全固溶于基体,负面影响基本消除。