外文翻譯---離子滲氮對(duì)馬氏體時(shí)效鋼微觀結(jié)構(gòu)和性能的影響 英文

1、Effect of ion nitriding on the microstructure and properties of Maraging steel (250 Grade)Kishora Shetty a,?, S. Kumar b, P. Raghothama Rao aa Regional Centre for Military Airworthiness (Foundry and Forge), CEMILAC, DRDO

2、, Bangalore-560 037, India b Department of Materials Engineering, Indian Institute of Science, Bangalore-560 012, Indiaa b s t r a c t a r t i c l e i n f oArticle history:Received 25 June 2008Accepted in revised form 28

3、 November 2008Available online 10 December 2008Keywords:Ion nitridingMaraging steelMicrostructureCase depthTensile propertiesFatigue propertiesIn the present investigation, ion nitriding of Maraging steel (250 grade) has

4、 been carried out at threedifferent temperatures i.e., at 435 °C, 450 °C and 465 °C for 10 h duration in order to achieve good wearresistance along with high strength required for the slat track component

5、of aircraft. The microstructure ofthe base material and the nitrided layer was examined by optical and scanning electron microscope, andvarious phases present were determined by X-ray diffraction. Various properties, suc

6、h as, hardness, casedepth, tensile, impact, fatigue properties and corrosion resistance were investigated for both un-nitrided andion-nitrided materials. It is observed that the microstructure of the core material remain

7、s unaltered and Fe4Nis formed in the hardened surface layer after ion nitriding at all the three temperatures employed. Surfacehardness increases substantially after ion nitriding. Surface hardness remains almost the sam

8、e but case depthincreases with the increase in ion nitriding temperature due to greater diffusivity at higher temperatures.Tensile strength, fatigue strength and corrosion resistance are improved but ductility and energy

9、 absorbed inimpact test decrease on ion nitriding. These results are explained on the basis of microstructuralobservations. The properties obtained after ion nitriding at 450 °C for 10 h are found to be optimum when

10、compared to the other two ion nitriding temperatures.© 2008 Elsevier B.V. All rights reserved.1. IntroductionSurface engineering means ‘engineering the surface’ of a material orcomponent to confer surface properties

11、, which are different from thebulk properties of the base material [1]. The purpose may be to reducewear, minimize corrosion, increase fatigue resistance, reduce frictionalenergy losses, act as a diffusion barrier, provi

12、de thermal insulation,exclude certain wave lengths of radiation, promote radiation, electronicinteractions, electrically insulate or simply improve the aestheticappearance of the surface. Surface engineering processes ma

13、y broadlybe grouped in three categories as (a) modifying surfaces without alteringthe substrate's chemical composition; these types of processes includetransformation hardening, cold deformation, machining and peenin

14、g,(b) changing the chemistry of the surface region; these types ofprocesses include carburizing, nitriding, anodizing and ion implanting,and (c) adding a layer of material to the surface; these types of processesinclude

15、weld overlay, painting, metal spraying, plasma spraying,electroplating, bonding, physical vapor deposition and chemical vapordeposition. Nitriding is a surface-hardening process by the introductionof nitrogen into the su

16、rface of steel [2]. Process methods for nitridinginclude gas nitriding, liquid or salt bath nitriding and plasma or ionnitriding. In gas nitriding this is done using a mixture of ammonia gasand dissociated ammonia in sui

17、table proportions. In plasma or ionnitriding a glow discharge technology is used to introduce nascent(elemental) nitrogen to the surface of a metal part for subsequentdiffusion into the material [3–5]. The plasma assiste

18、d surface modifica-tion techniques offer a great flexibility and are capable of tailoringdesirable chemical and structural surface properties independent of thebulk properties [3]. It has other advantages, such as, no or

19、 very thinwhite layer forms after nitriding and there is no machining or grindinginvolved after the process, which is particularly beneficial for complexparts. The hardened surface layer becomes an integral part of the b

20、asematerial and there is no significant reduction in properties of the basematerial. It is also known to provide the modified surface withoutdimensional change and distortion of the component. Ion nitridingprovides bette

21、r control of case chemistry and uniformity [3,6,7].Maraging steels belong to a new class of high strength steels withthe combination of strength and toughness that are among thehighest attainable in general engineering a

22、lloys [8]. The termmaraging is derived from martensite age hardening and denotes theage hardening of a low carbon, iron–nickel lath martensite matrix[9,10]. These steels typically have very high nickel, cobalt andmolybde

23、num and very low carbon content. They are strengthenedby the precipitation of intermetallic compounds at a temperature ofabout 480 °C [11,12]. Carbon is treated as an impurity and is kept aslow as commercially feasi

24、ble (b0.03 wt.%) in order to minimize theformation of titanium carbide (TiC), which can adversely affectSurface fax: +91 80 25236516.E-mail address: kishora_shetty@yahoo.com (K. Shetty).0257-8972/$ – see front matter &#

25、169; 2008 Elsevier B.V. All rights reserved.doi:10.1016/j.surfcoat.2008.11.034Contents lists available at ScienceDirectSurface & Coatings Technologyjournal homepage: www.elsevier.com/locate/surfcoat20 mm gauge length

26、 using TIRA Test 2820S Universal Testing Machine.Impact tests were conducted on Charpy ‘U’ notch specimens having adimension 10 mm?10 mm?55 mm using FIE Charpy Impact Testingmachine. Constant amplitude LCF tests were car

27、ried out on smoothround specimens with 4.5 mm gauge diameter and 12 mm gaugelength using Zwick Roell Universal Testing Machine at an appliedstress range of ±1172 MPa having stress ratio of ?1. Hardness valueswere me

28、asured at five places for each sample, for tensile and impactthree samples were tested at each condition and for LCF five sampleswere tested at each condition and the average value along withstandard deviation is reporte

29、d. Corrosion tests were carried out onspecimens having a dimension 10 mm?10 mm?18 mm for un-nitrided samples and 10 mm?10 mm?20 mm for ion-nitridedsamples using 5% NaCl solution for 144 h in a salt spray test chamber.3.

30、Results and discussions3.1. Microstuctural examinationOptical and scanning electron micrographs of un-nitrided and ion-nitrided specimens are shown in Figs. 3 and 4. These micrographs showa case hardened nitrided layer a

31、nd martensitic core structure. Thethickness of the nitrided layer increases with the increase in ionnitriding temperature due to greater diffusivity at higher temperatures.XRD patterns obtained from the surface of un-nit

32、rided and ion-nitrided specimens are shown in Fig. 5. The un-nitrided specimenexhibits diffraction peaks only due to Fe, whereas the ion-nitridedspecimens exhibit additional peaks due to Fe4N as well. The intensityof the

33、 Fe peaks progressively decreases and the intensity of the Fe4Npeaks progressively increases with the increase in ion nitridingtemperature. Thus, the iron nitride formed in the surface hardenedlayer on ion nitriding is F

34、e4N. The ratio of H2 and N2 in the gas mixtureused for ion nitriding in our investigation is 3:1, which is termed as γ′gas and forms mono phase (called as γ′ phase) crystal structure ofFe4N in the compound layer. Nitroge

35、n atoms go in to the interstitialsites of iron lattice in an ordered manner and form Fe4N [14].3.2. Hardness and case depthThe hardness values obtained on un-nitrided and ion nitridedsamples are given in Table 2. The ave

36、rage surface hardness of the un-nitrided samples is 616 VHN. The average surface hardness of thesamples ion nitrided at three different temperatures is more or less thesame and is about 50% higher than the un-nitrided sa

37、mple. HardnessFig. 3. Optical micrographs of (a) un-nitrided specimen, (b) ion nitrided at 435 °C, (c) ion nitrided at 450 °C and (d) ion nitrided at 465 °C.1532 K. Shetty et al. / Surface & Coatings T