A study of the mechanisms of fatigue life improvement in an ion implanted nickel-chromium alloy

Wires of the alloy Ni20Cr with and without carbon ion implantation have been tested in tension-tension fatigue. A 17% increase in endurance limit was found with implantation. The fatigued surface was examined by SEM, and the wire then nickel plated so that transverse sections could be made for TEM study. It was found that bulk slip was unaffected by implantation but slip in surface grains was unable to penetrate the implanted layer to significant degree. Slip band cracking which was found in unimplanted specimens was replaced by grain boundary cracking in the implanted specimens.     

Influence of annealing on depth distributions and microstructure of ion-implanted Ti6Al4V

Ti6Al4V alloy was ion implanted with carbon, nitrogen, platinum, or gold. The effect of heat treatment at 500°C on the depth distributions of oxygen and implanted atoms was investigated using backscattering spectrometry. The phases in the near-surface region were determined using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Platinum and gold are enriched in both α- and β-titanium solid solutions. Implanted carbon forms titanium carbide at lower concentration than nitrogen forms titanium nitride. The depth profiles of Au, Pt, and N are not altered by annealing. Implanted carbon as well as oxygen diffuse to larger depth upon heat treatment. Noble metal-implanted layers are permeable to oxygen diffusion. At concentrations exceeding 35 at. pct, implanted carbon and nitrogen act as a diffusion barrier for oxygen.     

氮离子束辅助电弧离子镀对TiN膜层中金属“大颗粒”影响的研究

采用俄罗斯UVN 0.5D2I离子束辅助电弧离子镀沉积设备,在高速钢W18Cr4V基材上沉积TiN膜层。研究了N离子束轰击能量对膜层表面形貌、相结构、显微硬度的影响。结果表明:N离子束辅助轰击,能够有效地减少和降低膜层表面"大颗粒"的数量和尺寸,消除了膜层中较软Ti2N相,得到了单一的TiN相。随着轰击能量的增加,TiN相结构不发生改变,TiN(111)取向逐渐减弱,而(200)取向逐渐增强。N离子束辅助轰击能量的增加,提高了膜层的显微硬度。     

Correlation of 3d transition metal carbide phase formation with 3d electrons by carbon ion implantation

A systematic study of carbide phase formation by carbon ion implantation showed NaCl type f.c.c. carbide formation in Ti, V and Cr, and hexagonal carbide formation in Fe, Co and Ni. No carbide formation was observed in the system Cu, Ag, Au and Zn. This indicates that 3d transition metal carbide phase formation by carbon ion implantation correlates with incomplete 3d shell electrons. The s shell electrons do not contribute. The electronic factor was further demonstrated in the structural alternation from f.c.c. in systems of Ti, V and Cr to hexagon in Fe, Co and Ni with increasing 3d electron concentration, which follows the Hume-Rothery rule.     

钛合金等离子体源离子注入表面改性

等离子体源离子注入技术是一种新型的非视线的离子注入材料表面改性技术. 为了对该项技术的表面改性效果进行科学的论证, 从而为该项技术的推广提供客观的试验依据, 采用该项技术对Ti6A14V合金进行氮离子注入, 对注入层的成分、组织和性能进行了分析. 结果表明： 注入层中氮浓度的分布具有类高斯分布特征;在注入层中有TiN和非晶态相形成;注入层的显微硬度和摩擦性能得到了明显的改善.     

Effects of simultaneous boron and nitrogen implantation on microhardness and fatigue properties of Fe-13cr-15ni alloys

Eight complex austenitic stainless steel alloys based on the composition Fe-13Cr-15Ni-2Mo-2Mn-0.2Ti-0.8Si-0.06C were implanted simultaneously with 400-keV B+ and 550-keV N⁺ ions and were investigated for changes in fatigue properties and surface microhardness. The nearsurface hardness of all eight alloys improved, but the fatigue life of each decreased. These findings were contrary to those obtained in an earlier study using four simple Fe-13Cr-15Ni alloys, where the dual implantation improved fatigue life by up to 250 pct. While unimplanted specimens failed by slip-band crack initiation, it was hypothesized that the dual implantation suppressed slip to the extent that fewer slip-band cracks were initiated and these were subjected to accelerated crack propagation. In addition, grain-boundary cracking was promoted, yielding a lower fatigue life. Support for this hypothesis was obtained by a study of single crystals of Fe-15Cr-15Ni, which were also implanted with B⁺ and N⁺. The dual implantation caused a lower fatigue life due to concentration of slip along a few slip bands to relieve applied stress. Evidence of grain-boundary cracking was obtained using the four simple alloys, which were subjected to triple ion implantation with B⁺, N⁺, and C⁺. The triple implantation decreased the fatigue life of the alloys and caused accelerated growth of fewer slip bands and grain-boundary cracking due to suppression of surface slip bands. This study thus shows the existence of an optimum level of strengthening when multiple ion implantation is used to improve the fatigue properties of alloys.     

Surface Modification by Nitrogen Plasma Immersion Ion Implantation on Austenitic AISI 304 Stainless Steel

Surfaces of AISI 304 austenitic stainless steel plates nitrided by plasma immersion ion implantation (PIII) technology were studied by means of Auger electron spectroscopy (AES)and X-ray photoelectron spectroscopy (XPS)to determine the effect of the nitriding process on the surface and subjacent layers.Elemental compositions obtained by AES and XPS at varying depths indicate that the saturation of N is relatively constant as a function of depth,indicating the reliability of PIII technology for subsurface saturation.It is concluded that the concentrations of both Cr and O increase with depth,the subjacent oxide is driven by the Ar+ sputtering process used to access the lower layers,and then N is bound to Cr.     

Improved oxidation resistance of group VB refractory metals by Al+ ion implantation

Aluminum ion implantation of vanadium, niobium, and tantalum improved the metals’ oxidation resistances at 500 °C and 735 °C. Implanted vanadium oxidized only to one-third the extent of unimplanted vanadium when exposed at 500 °C to air. The oxidative weight gains of implanted niobium and tantalum proved negligible when measured at 500 °C and for times sufficient to fully convert the untreated metals to their pentoxides. At 735 °C, implantation of vanadium only slightly retarded its oxidation, while oxidative weight gains of niobium and tantalum were reduced by factors of 3 or more. Implanted niobium exhibited weight gain in direct proportion to oxidation time squared at 735 °C. Microstructural examination of the metals implanted with selected fluences of the 180 kV aluminum ions showed the following. The solubility limit of aluminum is extended by implantation, the body centered cubic (bcc) phases being retained to ～60 at. pct Al in all three metals. The highest fluence investigated, 2.4 × 10²² ions/m², produced an ～400-nm layer of VAl₃ beneath the surface of vanadium, and ～300-nm layers of an amorphous phase containing ～70 at. pct Al beneath the niobium and tantalum surfaces. All three metals, implanted to this fluence and annealed at 600 °C, contained tri-aluminides, intermetallic compounds known for their oxidation resistances. Specimens implanted to this fluence were thus selected for the oxidation measurements.     

( Tb,Dy) Fe2合金表面离子注入渗氮改性及抗腐蚀性能研究

采用离子注入技术在(Tb,Dy)Fe2稀土超磁致伸缩材料表面引入氮离子进行改性处理,研究了加速电压对材料表面相结构、微观形貌、表面硬度、抗酸碱腐蚀性能及磁致伸缩性能的影响.结果表明:离子注入渗氮后,(Tb,Dy)Fe2合金表面的REFb相分解,生成了REN,α-Fe和Fe8N新相,材料表面微观形貌发生了明显变化,表面硬度明显提高.通过测试极化曲线研究了渗氮前后(Tb,Dy)Fe2合金在不同PH值NaCl溶液中的抗酸碱腐蚀性能,发现pH值相同条件下渗氮处理后(Tb,Dy) Fe2合金的自腐蚀电位Ecorr较渗氮前明显正移且有钝化现象发生.在加速电压140 kV,离子注入剂量5.0×1017 ion.cm -2条件下渗氮处理的(Tb,Dy)F合金,处于20℃,3.5％ NaCl溶液环境中,pH=4时,△Ecorr=0.23413 V; pH =7时,△Ecorr =0.18992 V; pH=10时,△Ecorr =0.01268 V,渗氮处理后(Tb,Dy)Fe2合金的抗酸腐蚀性能明显增强,抗碱腐蚀性能变化不明显.随着pH值的增大,渗氮与未渗氮(Tb,Dy) Fe2合金的抗腐蚀性能均变差.由于离子注入表面渗氮的渗氮层很薄,渗氮温度很低,渗氮处理没有破坏材料的内部基体结构,因此渗氮后材料渗氮处理没有破坏材料的内部基体结构,其磁致伸缩性能几乎未受影响.研究表明离子注入渗氮是(Tb,Dy)Fe2磁致伸缩材料表面改性的一种有效方法.     

Microdistribution of cerium in steel

Further experiments have been made to ascertain the conditions under which the method previously developed by the authors for determining the content of rare earth metals alloyed in steels can be applied. The accuracy of the results provided by this method is very satisfactory. The content of Ce alloyed in AISI 1518, AISI 1524 + B + Ti, SAE EV15, AISI Tl, and INCOLOY MA956 in the as-cast state have been determined. Autoradiographic studies show that Ce dissolves to a greater extent in pearlite than in ferrite in steels AISI 1518 and AISI 1524 + B + Ti. When Ce contents in the heat-resistant alloy INCOLOY MA956 and in SAE EV15 steel are high, the Ce segregate along grain boundaries. The content of Ce differs between grains; i.e., its distribution in steel is microscopically inhomogeneous.     

Effect of Yttrium Pre-Implantation on Implantation Behavior of Ti-6Al-4V Alloy in Nitrogen Plasma Immersion Ion Implantation

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超级双相不锈钢00Cr25Ni7Mo3.5N表面原位氧化研究

 采用高温XRD技术研究了超级双相不锈钢00Cr25Ni7Mo3.5N表面原位氧化行为。对该钢种在空气条件下进行连续加热,选取一些温度点进行测试,研究了其表面氧化物的生长规律,并分析了第二相的析出行为。结果表明, 600 ℃以下表面组织均为α、γ两相结构。800 ℃时α相开始被氧化成α Fe2O3,900 ℃时α相被氧化成α Fe2O3和Fe3O4,继续加热至1000 ℃时α相全部氧化消失。即使温度升高到1100 ℃,γ相也没有被氧化。而在空气条件下,不同温度水淬样品内部的室温组织始终保持α、γ两相结构,并且随温度增加,α相比例逐渐增加。此外,加热过程中还发现表面与内部的σ相几乎同步产生和消失。     

Assessment of CpTi Surface Properties after Nitrogen Ion Implantation with Various Doses and Energies

Nitrogen ion implantation is one of the surface modification techniques used for increasing corrosion resistance of commercially pure titanium (CpTi). The nitrogen ion implanted CpTi in various doses markedly changes the corrosion resistance. Still the effect of nitrogen ion implantation on the CpTi at different energies needs to be verified. This study uses different methods to assess the CpTi surface properties after nitrogen ion implantation in various doses and energy. Surface hardness of the CpTi increases with an increase of the dose and decreases with an increase of the energy. The precipitation of the TiN increases with an increase of the nitrogen dose, and no formation of the Ti₂N phase clearly appears. Corrosion resistance of the CpTi specimens can be upgraded to some extent after their surfaces are modified, implanting nitrogen ions at 100?keV by increasing dose. The optimum surface properties of the implanted CpTi are analyzed to contribute to materials science technology.     

Surface modification of （Tb,Dy）Fe_2 alloy by nitrogen ion implantation

Effects of nitriding modification on surface phase structure, morphology, corrosion resistance and magnetostriction of (Tb,Dy)Fe2 alloy were investigated by nitrogen ion implantation. Results showed that the surface REFe2 phase gradually decomposed and transformed into REN, α-Fe and Fe8N phases with the increase of nitrogen ion implantation dose. The surface morphology of the alloy had an obvious change after nitrogen ion implantation. The corrosion resistance properties of the alloy in acidic, alkaline and chloridion environment were also greatly improved. In addition, the magnetostriction performance of the alloy was almost not affected by ion implantation as the nitrided layer was quite thin and the operating temperature was very low. The results proved that nitrogen ion implantation was an effective method for surface modification of (Tb,Dy)Fe2 alloy.     

Effects of Hydrogen Ion Implantation on TiC-C Coating of Stainless Steel

Titanium carbide coatings are widely used as various wear-resistant material.The hydrogen erosion resistance of TiC-C films and the effect of hydrogen participation on TiC-C films were studied.Seventy-five percent TiC-C films are prepared on stainless steel surface by using ion mixing,where TiC-C films are deposited by rf magnetron sputtering followed by argon ion bombardment.The samples are then submitted to hydrogen ion implantation at 1.2×10-3 Pa.Characterization for the 75% TiC-C films was done with SIMS,XRD,AES,and XPS.Secondary ion mass spectroscopy (SIMS) was used to analyze hydrogen concentration variation with depth,X-Ray diffraction (XRD) was used to identify the phases,and Auger electron spectra (AES) as well as X-ray photoelectron spectra (XPS) were used to check the effects of hydrogen on shifts of chemical bonding states of C and Ti in the TiC-C films.It is found that TiC-C films on stainless steel surface can prevent hydrogen from entering stainless steel.     

干湿交替环境下气体组成对低合金钢腐蚀行为的影响

参照国际海事组织(IMO)所规定的模拟货油舱上甲板(COT)试验条件,利用专门建立的模拟上甲板环境腐蚀试验装置,研究了货油舱上甲板环境中,不同气体成分对低合金钢的腐蚀行为的影响.观察了低合金钢在不同成分的气体中基体和腐蚀产物的宏观和微观形貌,测定了锈层的物相组成.研究结果显示,在干湿交替环境下,低合金钢在SO2+ CO2+O2+N2气体中的腐蚀速率是H2S+ N2气体中的5.7倍;H2S+ N2环境下腐蚀产物为FeS,SO2+CO2+ O2+ N2环境下腐蚀产物为α-FeOOH、Fe2O3、FeSO4,且基体表面存在沿晶界发生的沟渠状和酸性液滴造成的斑状腐蚀形貌.     

Characterization of the solidification structures within the dendritic core of M2 high speed steel

The phases which are present within the dendritic core region during the solidification of AISI type M2 high speed steel (6 W, 5 Mo, 4 Cr, 2 V) were studied and characterized by metallography and quantitative microprobe analysis. A series of samples were quenched from various temperatures during solidification, “freezing in” the different solidification phases. The first phase observed to solidify in M2 is ferrite which contains very little carbon. As the solidification process continues, most of the liquid surrounding the ferrite transforms to austenite by virtue of a peritectic reaction which initiates at 1330°C,(L + F →A). The ferritic cores also transform at around 1330°C into an austenite plus car-bide aggregate. By the time the ingot cools to 1255°C, the carbides at the center of the dendrites dissolve completely, leaving an austenitic phase of uniform carbon and alloy content. At temperatures below the solidus, very fine carbides precipitate from the aus-tenite. No eutectoid decomposition by products such as those commonly observed in Tl tool steel were observed in these specimens nor in samples from a commercial ingot. JAMES McLAUGHLIN, formerly Graduate Assistant at Lehigh University     

Effect of phosphorous surface segregation on iron-zinc reaction kinetics during hot-dip galvanizing

Phosphorous was ion implanted on one surface of a large grain (10 to 20 mm) low-carbon steel sheet in order to study the effect of surface segregation on the formation of Fe-Zn phases during galvanizing. Both an Al-free and a 0.20 wt pct Al-Zn bath at 450 °C were used in this investigation. It was found that P surface segregation did not affect the kinetics of Fe-Zn phase growth for the total alloy layer or the individual Fe-Zn gamma, delta, and zeta phase alloy layers in the 0.00 wt pct Al-Zn baths. In the 0.20 wt pct Al-Zn bath, the Fe₂Al₅ inhibition layer formed with kinetics, showing linear growth on both the P-ion implanted and non-P-ion implanted surfaces. Fe-Zn phase growth only occurred after extended reaction times on both surfaces and was found to directly correspond to the location of substrate grain boundary sites. These results indicate that P surface segregation does not affect the growth of Fe-Zn phases or the Fe₂Al₅ inhibition layer. It was shown that in the 0.20 wt pct Al-Zn bath, substrate grain boundaries are the dominant steel substrate structural feature that controls the kinetics of Fe-Zn alloy phase growth.     

Redistribution of carbon in the deformation of steel with bainite and martensite structures

Recent years have been marked by considerable increase in the use of high-strength steel—especially martensitic and bainitic steel—for the manufacture of key industrial components and structures. The high strength depends on strain hardening of the steel. It is important to understand the strain hardening of steel of different structural classes with active plastic deformation, in order to ensure specified structural and phase states and mechanical properties. In the present work, by transmission electron-diffraction microscopy, the evolution of the structure, the phase composition, and the state of the defect substructure is compared for steel samples with martensite and bainite structure in active plastic deformation to failure. After austenitization at 950°C (1.5 h) and subsequent quenching in oil (for 38KhN3MFA steel) and cooling in air (for 30Kh2N2MFA steel), multiphase structure (α phase, γ phase, and cementite) based on packet martensite (38KhN3MFA steel) and lower bainite (30Kh2N2MFA steel) is formed. Quantitative results for the structural parameters of steel in plastic deformation permit analysis of the distribution of the carbon atoms in the structure of the deformed steel. The points of localization of carbon atoms in the martensite (quenched 38KhN3MFA steel) and bainite (air-cooled 30Kh2N2MFA steel) are identified. Deformation of the steel is found to be accompanied by the destruction of cementite particles. For quenched martensitic steel, the total quantity of carbon atoms in the solid solution based on α and γ iron is reduced, while their content at structural defects is increased. The redistribution of carbon atoms in the bainitic steel with increase in the strain involves the increase in the quantity of carbon atoms in the α iron, defects in the crystalline structure, and cementite at the intraphase boundaries; and the decrease in the content of carbon atoms in the cementite particles within the bainite plates and the γ iron.     

Effect of rare-earth doping on adsorption of carbon atom on ferrum surface and in ferrum subsurface: A first-principles study

The adsorption of carbon atom on Fe surface and in Fe subsurface with and without rare earth (La and Ce) substitution in the surface layer and subsurface layer was studied by first-principles calculations. The carbon atom is predicted to adsorb at hollow and long bridge site on Fe(100) and Fe(110), respectively. However, the carbon atom shifts to occupy preferentially hollow site on both Fe(100) and Fe(110) with rare earth atom doping at surface layer. The lower adsorption energies involved with stronger adsorption abilities were obtained for carbon atoms on Fe surface with rare earth doping at surface layer, which was determined by the electronic structure of the surface atoms. The La atom was pulled out the surface after carbon adsorption due to strong interaction of La–C, which is consistent with the more charge transfer. In the subsurface region, the carbon atom prefers to occupy at octahedral site with rare earth doping at surface layer in Fe slab. These strong adsorption energies of the carbon atoms on Fe surface and in Fe subsurface with rare earth pose relevant insights into the interaction between carbon and rare earth, which helps to understanding the influence mechanism of rare earth in carburizing.