【作者】 刘东华；

【导师】 黄伯云； 刘咏；

【作者基本信息】 中南大学 ， 材料学， 2010， 博士

【摘要】 铁基高温合金具有高的高温抗蠕变强度和抗中子辐射肿胀性能,是一类具有优越综合性能的先进结构材料。纳米氧化物弥散强化(ODS)铁素体合金的性能和制备工艺研究一直是许多科研学者努力的方向。本文通过直接氧化和雾化加氧两种方法制备铁基高温合金粉末Fe-14Cr-3W-0.5Ti-0.3Y-0.30(wt,%),并研究铁基合金粉末的氧化动力学以及氧在雾化粉末、球磨粉末和后续致密化合金中的存在形式；通过提高铁基合金粉末中第二相的百分含量,阐述了影响合金致密度和第二相形成的因素；采用热加工和热处理工艺获得了室、高温力学性能优良的铁基合金,分析并讨论了合金的微观结构演变规律和第二相对合金的强化机理,得到以下主要结论：(1)铁基合金雾化粉末Fe-14Cr-3W-0.5Ti-0.3Y-0.030(wt,%)在500℃进行氧化时,其氧化过程符合动力学方程(ΔW/S)2=kpt+c。氧化16h以内,氧化机制受表面反应控制。提高氧化温度并缩短氧化时间,可以抑制Fe203氧化层的长大。(2)氧以固溶形式存在于雾化粉末中；在氧化粉末中,氧达到扩散固溶度后直接在粉末颗粒表面聚集。在高能球磨过程中,粉末颗粒中产生大量晶格畸变,氧在粉末中的固溶度扩大,以固溶的方式存在于球磨粉末中。(3)合金Fe-14Cr-3W-0.5Ti-0.3Y-0.220(wt,%)在800～1000℃温度区间内烧结时,再结晶晶粒尺寸为亚微米级,这些晶粒非常稳定,尺寸随烧结温度和时间的变化不明显。1200℃退火基体中出现针、条状晶粒组织,延长保温时间会出现晶粒的异常长大现象,产生两种尺寸分布的晶粒,这是由于晶粒中Y-Ti-O第二相粒子分布不均匀导致的。球磨粉末锻造合金Fe-14Cr-3W-0.5Ti-0.3Y-0.220(wt,%)在温度为600和700℃时,获得了较好的耐摩擦性能,随着温度和滑动速度的提高,合金的磨损机制发生了改变,由粘着磨损转化为氧化磨损和磨粒磨损。(4)合金Fe-14Cr-3W-5Ti-3Y-2.2O(wt,%)中,析出相Ti2Y207对基体产生强化作用。随烧结温度升高,析出相发生长大,强化作用减弱。该锻造态合金的高温压缩强度不仅与弥散相粒子的大小有关,粒子的体积百分含量也起到了至关重要的作用。(5)铁基雾化粉末锻造态合金经1300℃退火,再结晶完全,晶粒细小,硬度值高达HRC54.8,随退火温度的提高,由于强化相颗粒长大,导致硬度值下降；经700℃低温回火处理后,由于材料中Cr的固溶度降低,铁基合金晶格常数变小,硬度值下降。(6)在铁基合金雾化粉末中引入不同的添加物,结果表明,添加A1粉加速了铁素体基体中的元素扩散,致使合金的晶粒尺寸增大；添加Fe203粉的合金由于O的固溶,氧化物溶解,产生大量残余孔隙,阻碍晶粒长大,因而晶粒尺寸较小。合金晶粒的长大规律满足Beck方程,添加Al粉合金的晶粒生长指数得到提高；添加Fe203粉合金的晶粒生长指数下降。(7)通过旋锻工艺可提高挤压态铁基合金的致密化程度,随着热处理时间增加,合金晶粒长大明显。Y-Ti-O纳米粒子对合金高温强度的稳定性起至关重要的作用,析出相粒子没有随退火时间的延长而发生长大,且在850℃下的压缩强度变化不明显。更多还原

【Abstract】 Fe-based superalloy which has high creep strength and neutron irradiation-resistance at high temperatures is one important kind of advanced materials. The major goal is to research the preparation process and the properties of the oxide diffusion strengthen (ODS) ferrite alloy. In this study, oxidation kinetics and the form of oxygen in the atomized powder, mechanical alloyed powder and the iron-based alloy Fe-14Cr-3W-0.5Ti-0.3Y-0.3O(wt,%) were researched by direct oxidation or oxygen addition by atomization; the factors that affect the compaction and the precipitation phase formation of the sintered alloy were represented through enhancing the content of the precipitated phase; the iron-based alloy with the excellent room and high temperature properties was manufactured by the hot working and heat treatment process, and the microstructure evolution and the strengthen mechanism were studied, then the conclusions are drawn as below:(1) The oxidation behavior of iron-based metal powder Fe-14Cr-3W-0.5 Ti-0.3Y-0.03O(wt,%) at 500℃has been studied. The oxidation process obeys the oxidation kinetics (ΔW/S) 2=kpt+c. Oxidation mechanism is controlled by surface reaction within 16 hours. The formation of the Fe2O3 oxide surface can be controlled by increasing the oxidation temperature and shortening time.(2) The existential manner of oxygen in the atomized powders is solid solution. The O dissolves uniformly in the oxidized powder and a very thin layer of oxides forms on the powder surface after sintering. The solid solubility of oxygen in the iron-based powder expands during the mechanical alloying process. The oxygen as solid solute is evenly distribution in the mechanical alloyed powders.(3) During sintering at temperatures from 800 to 1000℃, large number of equiaxed grains fine as hundreds of microns are found embedding in the matrix of Fe-14Cr-3W-0.5Ti-0.3Y-0.22O alloy (wt,%). The recrystallized grains are ultra-stable and show minor dependence on sintering temperature and time. When heated to high temperature, the recrystals turn to lamellar grained structure; while abnormal grain growth occurs after prolonged annealing and results in bimodally grained structure. The inhomogeneous distribution of Y-Ti-O nano-oxides throughout the matrix, which is the main reason of bimodally grained structure. The MA-ed Fe-14Cr-3W-0.5Ti-0.3Y-0.220 alloy (wt,%) shows the better friction properties at 600 and 700℃, and the wearing mechanism is changed from adhesive wear to oxide wear and abrasive wear with the temperature and sliding speed increasing.(4) The precipitated phase Ti2Y2O7 in the Fe-14Cr-3W-5Ti-3Y-2.2O (wt,%) alloy is the dispersion strengthen phase when the densification of the sintered alloy ended. The size of precipitated particle grows and the enhancing effect decreases with the increasing of the sintering temperature. The high temperature compressibility strength is associated with the precipitated particle size and the weight percentage of the particles in the forged alloy. The hardness of the forged alloy by using atomized powder is HRC54.8 at 1300℃, because the grains occur full recrystallization, and the grain size becomes fine. The hardness decreases with annealing temperature increasing, because the grain size of recrystallization unchanged but softening occurred. After tempering at 700℃, crystal size changed unobvious, the hardness value decreases which is because of the decrease of solid solubility of Cr.(5) The results show that the addition of Al facilitates its diffusion in the iron-based alloy and the grain size of the alloy is largest among the iron-based alloy with additions. The alloy adding Fe2O3 also has some residual porosity left by the solution of the oxide which hinders the grain growth. Grain growth obeys the Beck equation. Adding Al increases the grain growth exponent while adding Fe2O3 decreases the grain growth exponent.(6) The high density iron-based alloy has been prepared by swaging process. The grain size of the alloy growths with the heat treatment temperature increasing. The Y-Ti-O nano-oxides play a vital role in the stable of the high temperature strength. The precipitated particle size show minor dependence on annealing temperature and time. The compressibility strength at 850℃remains constant.更多还原