The influence of atomic order on H2-induced environmental embrittlement of Ni3Fe intermetallics

The different sensitivity to H₂-induced environmental embrittlement for the ordered and disordered Ni₃Fe alloys has been investigated. The results show no environmental embrittlement in disordered Ni₃Fe in gaseous H₂ when tested at room temperature. However, the H₂-induced environmental embrittlement for the ordered Ni₃Fe becomes severer as the degree of order increases. The results of testing on simultaneous hydrogen charging show that disordered Ni₃Fe embritted as hydrogen atoms are forced into the material, implying that the embrittlement of ordered Ni₃Fe in gaseous H₂ is due to the acceleration of the kinetics of catalytic reaction to produce more atomic hydrogen. Further more, the hydrogen adsorption test of Ni₃Fe powder shows that the amount of chemically adsorbed hydrogen in the ordered state at room temperature is significantly larger than that adsorbed by the disordered materials, indicating that the more sensitive to H₂-induced embrittlement in the ordered Ni₃Fe is essentially due to accelerated catalytic reaction to produce more atomic hydrogen.     

The effect of atomic ordering on the hydrogen absorption and desorption of Ni4Mo alloy

Hydrogen absorption and desorption of disordered and ordered Ni₄Mo alloys were investigated. The results show that the atomic ordering can promote gaseous hydrogen absorption at room temperature and therefore exacerbates the hydrogen gas-induced environmental embrittlement.     

Effect of atomic ordering on environmental embrittlement of （Co,Fe）3V alloy in gaseous hydrogen

The diffusible hydrogen contents in precharged(Co,Fe)3V alloy were measured.It is found that atomic ordering can not promote hydrogen peretration in the(Co,Fe)3V alloy.The ultimate tensile strength(UTS)and ductilities in various condition were also investigated.The results show that the UTS and elongation of disordered alloy are higher than that of ordered one with fixed diffusible hydrogen content and(Co,Fe)3V alloy with ordered structure is highly sus ceprible to the embrittlement in hydrogen gas.The factor which may affect the susceptibility to the embrittlement of (Co,Fe)3V alloy in hydrogen gas in mainly due to that the atomic ordering may accelerate the kinetics of the catalytic reaction for the dissociation of molecular hydrogen into atomic hydrogen.However,it can not be roled out that atomic ordering intensifies planar slip and restricts cross-slip at the grain boundaries and enhances the suscptibility of the alloy to hydrogen embrittlement.     

Moisture and hydrogen-induced embrittlement of iron aluminides

It is now apparent that Fe₃Al and FeAl alloys with less than 40 at.% Al are intrinsically ductile. Brittleness is manifested only in environments providing ready access to hydrogen. Microstructure, alloy content and surface condition may alter somewhat the susceptibility to embrittlement by moisture or by hydrogen, but are key considerations in alloy design for toughness or ductility when aluminum content is within the Fe₃Al-FeAl range. The susceptibility of iron aluminides to moisture and to hydrogen is a major factor hampering their development as structural alloys. Other properties which need to be improved include tensile strength and creep and impact resistance, but approaches to achieve improved strength properties must consider the susceptibility to the external environment. Development of alloys with less than 16% Al appears to be attractive for situations where reduced strength and oxidation resistance can be tolerated because of the insensitivity of these alloys to embrittlement. However, it must be realized that these alloys are not intermetallics.     

Effect of atomic ordering on the phase transformations in Ni–Mn–Ga shape memory alloys

The influence of the L2₁ order degree in single crystalline Ni–Mn–Ga alloys is analysed in the present work. The alloys studied display a sequence of martensitic (MT) and intermartensitic (IMT) transformations on cooling, the reverse transformation to austenite, on heating, taking place in a single step. Quenching from different temperatures produces distinct effects on the MT and IMT: while the MT temperatures are not practically affected by the performed heat treatments, the IMT shifts towards lower temperatures after quenching from increasing temperatures. Such evolution can be related to changes in the L2₁ order degree, in the sense that ordering favours the occurrence of the IMT while it hardly affects the MT temperatures. The closeness of the free energies of the different martensitic structures and the differences between the MT and IMT entropy changes allow this behaviour to be explained. In turn, the Curie temperature increases with the L2₁ ordering for an alloy undergoing magnetic transition in martensite phase, no changes being detected if the Curie temperature is above the martensitic transformation.     

Lattice gas decomposition model for vacancy formation correlated with B2 atomic ordering in intermetallics

Thermal vacancy formation correlated with atomic ordering was modelled in B2-ordering A–B binary intermetallics. Ising Hamiltonian was implemented with a specific Bragg–Williams-type thermodynamic formalism for thermal vacancy formation based on the phase equilibria in a lattice gas composed of atoms and vacancies. It has been demonstrated that for pair-interaction energetics favouring vacancy formation on A-atom sublattice, equilibrium concentrations of vacancies and antisite defects result mutually proportional in well defined temperature ranges. The effect observed in both stoichiometric and non-stoichiometric binary alloys was interpreted as a tendency for triple defect formation. In B-rich non-stoichiometric binary alloys vacancy concentration did not extrapolate to zero at temperature approaching zero, which indicated the formation of constitutional vacancies. Energetic conditions for the occurrence of the effects were analysed in detail.     

Processes of atomic ordering in microcrystalline ternary alloys based on Ni3Mn

Stable and metastable phases are formed in the production of microcrystalline alloys By quenching from the melt, The atomic ordering of these phases has not been completely studied until recently. In ternary systems with two ordered phases having different Kurnakov temperatures TK (the temperature of the order-to-disorder transition), for example, an intetmetallic compound and an ordinary superstructure, preferential formation of a superstructure with a highT _K is expected and the alloying atoms occupy vacancies in the ordered lattice of the intermetallic compound. The present work concerns neutron diffraction analysis of atomic ordering in the ternary systems Ni₃Mn-Ni₃Al, Ni₃Mn-Ni₃Si, and Ni₃Mn-Ni₃Ti.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 2–4, August. 1995.     

退火工艺对镍/铝复合带金属间化合物的影响

研究了镍/铝复合带的退火热处理工艺,探讨了退火温度和时间对复合界面上金属间化合物生长的影响.结果表明:退火中温度过高会使界面上生成较厚的金属间化合物,退火温度在450～460℃时,镍/铝复合带的综合组织性能较为理想.当达到一定的热力学条件后,金属间化合物首先在界面局部区域生成并迅速完成长大,随退火时间延长,各区域的化合物新生相沿界面连接为一个整体.延长退火时间对金属间化合物层的相组成和各相厚度影响不大.综合复合带组织与性能的要求,得到优选退火工艺为460℃退火1h.     

Fe和Mo元素对TiAl金属间化合物显微组织和性能的影响(英文)

β相可以提高TiAl金属间化合物的塑性。通过显微组织分析和变形行为的评估研究β稳定性元素Fe和Mo对Ti-45Al-xFe-yMo(x,y=1,2,3,4)合金的影响。结果表明:合金中的B2(β)相随着Fe和Mo元素含量的增加而增多,Mo表现出强的β稳定性。加入3%Fe和2%Mo后,合金的晶粒得到细化,其尺寸达到12-m。由于具有一定量的β相,细化后的Ti-45Al-3Fe-2Mo合金在790℃具有良好的塑性。     

喷焊材料对OCr13Ni4Mo钢表面强化的影响

选用自熔合金粉末Ni60和Ni25B,采用氧－乙炔喷焊技术对0Cr13N4M钢的表面进行强化处理,并对喷焊层的组织、结合强度、硬度及耐磨性进行了研究,结果表明：两种粉末的喷焊层均与基体0Cr13Ni4Mo钢有良好的结合强度;喷焊层的硬度、抗磨损性均高于基体。     

Effect of microstructure on environmental embrittlement in a TiAl base alloy

The effect of different microstructure on environmental embrittlement in a chromium-containing TiAl alloy has been analyzed. The alloys having fully lamellar, nearly lamellar and duplex structure exhibited no apparent difference in the fracture strength and the tensile elongation at two test environments, vacuum and air. The near gamma alloy shows more strength higher and ductility in the vacuum than in the air. Tensile ductility increased to 3.5% in the vacuum, compared with 0.3% in the air. It can be argued that the gamma phase itself has relatively high intrinsic ductility, although a relationship with the ductility of alpha-2 is not yet clarified. An important factor to determine the environmental effect is the morphology and the volume fraction of alpha-2 phase in the alloy.     

孔结构对Ni3Al金属间化合物多孔材料抗腐蚀性能的影响（英文）

采用元素粉末反应合成的方法并用尿素作为造孔剂制备Ni3Al金属间化合物多孔材料。用电化学和浸泡实验表征Ni3Al金属间化合物多孔材料在6 mol/L KOH溶液中的抗腐蚀行为。系统研究孔结构对材料抗腐蚀性能的影响。研究结果表明:孔隙率较大的Ni3Al金属间化合物多孔材料较孔隙率较小的样品腐蚀更严重,这是由于孔隙率较大的样品具有复杂的联通孔结构以及较大的比表面积。然而,材料的腐蚀速率与比表面积并不成正比,这是因为随着孔隙率的增大,材料的孔径大小、孔径分布以及孔隙形状都随之变化。不同孔隙率大小的Ni3Al金属间化合物多孔材料在碱溶液中均表现出较好的抗腐蚀性能。     

复合化学热处理对G13Cr4Mo4Ni4V钢组织和硬度的影响

采用扫描电镜、洛氏硬度计和维氏显微硬度计研究了渗氮140 h对渗碳+淬火+回火G13Cr4Mo4Ni4V钢微观组织及硬度的影响。结果表明,渗碳+淬火+回火后G13Cr4Mo4Ni4V钢有效渗碳层深度为1.45 mm,渗碳层最高硬度为785 HV,心部硬度为420 HV,经渗氮处理后有效渗碳+渗氮层深度降为1.34 mm,渗氮层深度为0.22 mm,渗氮层最高硬度可达到948 HV,心部硬度为451 HV,较未渗氮试样硬度略有提高。渗碳+淬火+回火和添加渗氮处理后G13Cr4Mo4Ni4V钢的表面洛氏硬度相当,均在62~65 HRC 之间,但渗氮处理后试样的硬度波动性较大。添加140 h渗氮的渗碳+淬火+回火后G13Cr4Mo4Ni4V钢实现了“表面硬心部韧”的目标,渗氮层深度满足工程需要,但添加渗氮处理后G13Cr4Mo4Ni4V钢在渗碳层和渗氮层出现类网状碳化物,因此在渗氮过程中需要综合考虑渗氮层深度和微观组织,以获得良好的综合力学性能。     

氮对马氏体不锈钢00Cr13Ni4Mo组织和性能的影响

采用热膨胀仪、光学显微镜以及CM12型透射电子显微镜研究了添加0.04%N(质量分数)对00Cr13Ni4Mo马氏体不锈钢相变以及正火和回火后不锈钢组织变化的影响;通过拉伸、冲击实验和阳极极化曲线测定研究了N对正火和回火后马氏体不锈钢力学性能以及点蚀点位的影响。结果表明:1050℃正火后,N全部固溶于马氏体基体中,有效提高了实验钢的强度,同时降低了韧性;550℃以上回火后,在马氏体板条内部以及板条之间形成逆变奥氏体,有效提高了马氏体不锈钢的塑性和韧性;N抑制逆变奥氏体的形成,从而抑制了不锈钢在回火过程中的软化;同时,回火过程中,Cr2N在马氏体板条界面及内部大量析出,造成不锈钢韧性和点蚀点位下降。采用传统的正火+Ac1温度以上回火热处理工艺不利于含N马氏体不锈钢获得良好综合性能。     

Oxidation and embrittlement of Ti-6Al-2Sn-4Zr-2Mo alloy

Ti-6Al-2Sn-4Zr-2Mo titanium alloy is a candidate material for multiwall thermal protection system concepts for advanced space transportation system vehicles. The total oxidation kinetics for this alloy, exposed to laboratory air in the 593–760°C range, were monitored by thermogravimetric analysis. The oxide thickness was measured by microscopy and the substrate contamination was estimated from microhardness measurements. Tensile elongation was determined for selected foil specimens after exposure to simulated space shuttle reentry conditions. The variation of total weight gain with time was found to have two distinct parabolic stages separated by a transient region. This transient was due to a process which involved an increase in the parabolic growth rate constant for the oxide and a simultaneous increase in oxygen solubility at the oxide metal interface. The time dependent increase in oxygen solubility at the interface was from about 7 at. % in stage 1 to about 18 at. % in stage 2. The diffusion coefficient for oxygen in the alloy was determined as a function of temperature using the difference between the total weight gain in stage 1 and the corresponding weight gain due to oxide growth. A model for the total oxidation kinetics, accounting for the two individual components namely oxide growth and solid solution formation, is proposed. The activation energy for the diffusion of oxygen in the alpha-solid solution is shown to be roughly equal to the activation energy for the degradation of tensile elongation for the alloy in the foil gage condition.     

The effect of Nb addition on environmental embrittlement of a Ni3(Si,Ti) alloy

The effect of Nb addition on the moisture-induced embrittlement of a Ni₃(Si,Ti) alloy was investigated at room temperature by tensile test and SEM fractography. Embrittlement/ductility was assessed as functions of strain rate and environment. The Nb-containing second-phase dispersion was found to be effective in reducing the moisture-induced embrittlement of the Ni₃(Si,Ti) alloy, while Nb as a solute in the Ll₂ matrix was shown to enhance the moisture-induced embrittlement of the Ni₃(Si,Ti) alloy. Possible mechanisms accounting for the beneficial effect of the Nb-containing second-phase dispersion on the moisture induced embrittlement of the Ni₃(Si,Ti) alloy was discussed in terms of microstructural modification by the second-phase, hydrogen transportation kinetics and deformation properties in the constituent phases or L1₂ matrix/second-phase interface.     

Anelastic effects connected with isothermal martensitic transformations in 24Ni4Mo austenitic and 12Cr9Ni4Mo maraging steels

Anelasticity of the austenitic steel 24Ni5Mo and the stainless steel 12Cr9Ni4Mo has been investigated in the austenitic state after quenching with respect to isothermal martensitic transformation during cooling and subsequent heating. Maxima of anelasticity due to isothermal transformation at ≈200 K (24Ni5Mo, 0.002% C) and ≈250 K (12Cr9Ni4Mo; 0.01% C) coincided well with C-curve noses obtained by methods based on magnetic properties and electric resistivity. Corresponding internal friction maxima were found to be dependent on cooling or heating rate, quenching temperature and the frequency of oscillation and may therefore be described using the Delorme approximation. The activation energy of isothermal martensitic transformation calculated from the lower part of the C-curves estimated using the Borgenstam–Hillert and Arrhenius methods (3–8 kJ/mol for 24Ni5Mo and 15–20 kJ/mol for 12Cr9Ni4Mo) are comparable with the energy of impurity–dislocation interaction (≈10 kJ/mol) and interpreted as too low to be caused by diffusion processes: the activation energy for carbon diffusion in austenitic steel 24Ni5Mo is found to be ≈135 kJ/mol and ≈145 kJ/mol for austenite in two-phase 12Cr9Ni4Mo steel. An estimation showed that the activation energy for the isothermal martensitic transformation for the 24Ni5Mo alloy with so-called binary martensitic kinetics was higher in the vicinity of the nose of the C-curve, became lower with a decrease in temperature range and approached zero in the vicinity of the athermal martensitic point. A similar effect was not observed in the 12Cr9Ni4Mo steel.