Laves phase in Fe-Cr-Co alloys containing molybdenum and niobium

Conclusion Additional alloying of Fe–Co–Cr alloys containing molybdenum with niobium in an amount greater than 1% leads to formation of MgNi₂ type Laves phases in them, which markedly restrains grain growth during annealing in the temperature range 1000–1250°C.Institute of Steels and Alloys, Moscow. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, p. 58, January, 1987.     

Mechanism of adding rhenium to improve hot corrosion resistance of nickel-based single-crystal superalloys

Hot corrosion behavior in sulfate salt at 950℃of Rene N5 single-crystal superalloys with 3 wt% rhenium(NSR) was investigated compared with that of nickel-based single-crystal superalloys without rhenium(NS).After30-h corrosion,the surface of the NS superalloy is seriously corroded.Many holes and exfoliation appear on the surface.The NSR superalloys exhibit better hot corrosion resistance than the NS superalloys.After 30-h corrosion,a continuous and compact A1203 film is observed on its surface.The Al_2 O_3 film with dense structure formed on the surface provides protection for the matrix.The characterization results show that A1 is aggregated in the γ' phase,while Re is aggregated in the y phase during the formation of oxide scale.Considering that Re can inhibit the diffusion of A1 in the nickel matrix,it is inferred that Re can inhibit the outward diffusion of A1 and prevent the decrease of Al concentration in the γ' phase.High concentration of Al hinders the decomposition of Al_2 O_3 due to the reaction of acid and basic dissolution.Al_2 O_3 keeps its structure intact and provides protection for the matrix.     

The hardness and corrosion resistance of nickel alloys with molybdenum and tungsten

Conclusions The newly-developed Ni–Mo–W corrosion resistant hard alloys (N65M20V15 and N55M20V25) have a corrosion rate of no more than 0.2 mm/year in 30% HCl at 60°C and in 70% H₂SO₄ at 90°C, with a hardness as high as HRC 52.The alloys are precipitation-hardening. To obtain a high hardness it is recommended that they be heat treated by water quenching from 1000–1050°C and aging at 800°C for 4 h.Deceased.Central Scientific-Research Institute of Ferrous Metallurgy. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 24–27, March, 1972.     

The Oxidation of cobalt-tantalum base alloys containing carbon

The oxidation of cobalt-tantalum carbon alloys, containing 10 and 15 wt.% Ta and carbon in the range 0–1 wt%, was carried out in oxygen and air at atmospheric pressure at 900, 1000 and 1100°C. The alloys oxidised according to the parabolic rate law with activation energy of about 38 Kcal/mole. In general, the addition of tantalum decreases the oxidation rates, in comparison with cobalt and with the same mass of chromium added to cobalt. Again, the presence of carbon in the Co-Ta alloys decreases its oxidation rates in comparison with carbon-free alloys. The scales formed on Co-Ta and Co-Ta-C alloys consist mainly of an outer layer of cobalt oxide, CoO, and an inner porous layer of mixture of oxides: cobalt oxide; CoO, tantalum oxide; Ta₂O₅, and solid solution of these two oxides; CoTaO₄ at all temperatures in the range of 900°-1100°C. The binary Co ?10% Ta and Co ?15% Ta show an internal oxidation along the internal phase, increasing of alloy tantalum content increases the density of the internal phase. The presence of carbon in the ternary Co-Ta-C alloys has little effect and there is no apparent preferential penetration along the tantalum carbide network. In contrast to carbide present in Co-Cr-C alloys, where these carbides were preferentially attacked, the outer scale was disrupted, due to the formation of carbon gaseous oxides.     

High temperature corrosion behaviour of a gradient NiCoCrAlYSi coating II: Oxidation and hot corrosion

The high temperature oxidation and hot corrosion behaviour of a NiCoCrAlYSi coating and a gradient coating were investigated. The gradient coating showed better performance of re-healing alumina scale due to its possession of more β phase as Al reservoir. The degradation process of the gradient coating was favorably retarded by the formation of Cr(W)-rich σ precipitates in the interdiffusion zone. The corrosion results also confirmed an improved corrosion resistance of the gradient coating. The improved high temperature performance of the gradient coating owes to the Al enrichment of Al in the outer layer.     

Effects of molybdenum on the microstructure and wear resistance of nickel-based hardfacing alloys investigated using Rietveld method

The nickel-based hardfacing alloys with different Mo contents have been deposited on Q235-carbon steel using a plasma transferred arc (PTA) welding machine. The effects of Mo on the microstructure and wear resistance properties of the nickel-based hardfacing alloys were investigated using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). More detailed information about the crystallographic structure and phase compositions of the deposited coatings was obtained with the application of Rietveld refinement method to analyze XRD spectra. It was found that the addition of Mo did not lead to a change in phase compositions. Furthermore, it can also be seen that the relative contents of the total Cr-rich compounds increased from 36 wt.% to 45 wt.%, though the M₂₃C₆ type carbide increased but the relative contents of the M₇C₃ type carbide decreased with the increasing of Mo contents from 0 wt.% to 6 wt.%. The component segregation, which existed in the Mo-free coating, decreased gradually then disappeared finally with the increasing of Mo contents. The morphology of Cr-rich compounds observed in the interdendritic region changed from plate-like to net-like, as well as the refinement of Ni-rich dendrites because of the addition of Mo. The wear resistance increased but the microhardness decreased with the increasing of Mo contents from 0 wt.% to 6 wt.%. The microstructural change and phase contents variation were responsible for the improvement of the mechanical properties such as wear resistance of the Mo-modified nickel-based hardfacing alloy.     

Oxidation and hot corrosion behaviors of HVAF-sprayed conventional and nanostructured NiCrC coatings

The oxidation and hot corrosion behaviors of HVAF-sprayed conventional and nanostructured NiCrC coatings were studied. The oxidation experiment was conducted in air, and the hot corrosion was conducted in the Na₂SO₄–30%K₂SO₄ environment, in the temperature range of 550–750 °C for periods up to 160 h. The corrosion kinetics was tested with the thermogravimetric method. The corrosion products were characterized by scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffractometry (XRD). As indicated by the results, both types of coatings possess high corrosion resistance, especially the nanostructured NiCrC coating. The enhanced grain boundary diffusion in the nanostructured coating not only promotes the formation of a denser Cr₂O₃ scale with a higher rate, but also helps to mitigate the Cr depletion at the metal/scale interface. The less porosity of the nanostructured coating is also thought to be beneficial to the anti-corrosion properties.     

Ni-7Cr-4Al纳米复合镀层的氧化和热腐蚀性能(英文)

采用复合电镀技术,通过向普通硫酸镍电镀液中加入纳米Cr和Al颗粒,在Ni基材上制备了一种Ni-7Cr-4Al(质量分数,%)纳米复合涂层,对其在800°C下的空气氧化和750°C下75%Na2SO4+25%Na Cl混合熔盐热腐蚀性能进行研究。作为对比,对相同工艺制备的Ni-11Cr纳米复合镀层和纯Ni镀层的氧化和热腐蚀性能进行分析。Cr和Al纳米颗粒弥散分布在20~60 nm的纳米Ni中,与Ni-11Cr纳米复合镀层和纯Ni镀层相比,Ni-7Cr-4Al纳米复合镀层由于能快速形成氧化铝膜而表现出更优异的抗氧化性能,同时氧化铝膜的快速形成也提高了涂层的热腐蚀性能。     

Diffusion welding of nickel-based creep-resisting alloys

Special features of the diffusion welding of creep-resisting alloys were investigated to evaluate the possibilities and prospects of using these alloys in aviation engine construction.     

The mechanism of intergranular corrosion of dilute zinc-aluminium alloys in hot water

On the basis of polarization studies, grain boundary corrosion rate measurements and metallographic results, a corrosion mechanism is advanced which allows for a full explanation of the corrosion behaviour of zin—aluminium alloys. Explanations are provided for the well-known detrimental effects of lead additions, and the beneficial effects of copper and magnesium additions to these alloys.     

含钛Fe-Mn基减振合金的阻尼性能和耐蚀性能

用内耗检测技术研究了Ti对Fe-14Mn、合金Fe-17Mn和Fe-23Mn合金阻尼性能的影响和Ti对Fe-Mn系合金相组成和耐蚀性能的影响.结果表明:Fe-17Mn合金比Fe-14Mn和Fe-23Mn合金具有更高的阻尼性能;在Fe-Mn合金中加入1.0wt%左右的钛,合金的阻尼性能受到轻微影响;合金在固溶处理时,转变生成的ε马氏体越多,合金的阻尼性能越好;并且含钛合金对3%的NaCl溶液的耐蚀性能提高近2倍.     

Nitrogen-atomized,nickel-based,corrosion-resistant alloys

Nitrogen gas atomization has been used for many years to produce iron-based powder-metal materials such as stainless and tool steels. However, it is more typical to use argon atomization with nickel-based alloys because it avoids the formation of nitrides that, in some cases, can be detrimental to the mechanical properties of these materials. In this article, two nickel-based materials— alloy 625 and alloy 690—normally used for applications where corrosion resistance is of primary importance were evaluated in their nitrogen-atomized powder metal form. Nitrogen atomization uncovered attributes of these nickel alloys that are not present in their conventionally produced counterparts or in argon-atomized versions of the same compositions.     

弥散型高强度镍基高温弹性合金

采用真空中频熔炼、轧制加工及热处理研制出符合航空要求的高温镍铍钛合金带,各项性能达到了美国同类产品水平.