【摘要】：Nb-Si難熔合金的顯微組織通常包含鈮基固溶體(Nbss)和鈮硅化物(Nb_5Si_3/Nb_3Si),由于其高熔點、低密度和良好的高溫強度等優(yōu)點,成為極具潛力的滿足新一代航空發(fā)動機需求的高溫結(jié)構(gòu)材料。但目前廣泛應用真空電弧熔煉等鑄造方法制備的Nb-Si難熔合金因組織粗大和成分偏析等缺陷影響其性能,并且金屬間化合物的本征脆性也阻礙了Nb-Si難熔合金作為高溫結(jié)構(gòu)材料的實際應用。本文采用機械合金化+真空熱壓燒結(jié)相結(jié)合的粉末冶金方法制備了Nb-Si二元難熔合金以及不同Ti、Fe含量的Nb-Si多元難熔合金(Si含量16at.%),并通過粉末鍛造短流程技術(shù)成形了發(fā)動機推力室模擬件,研究了機械合金化過程中不同混合粉末系統(tǒng)的組織形貌變化以及在不同狀態(tài)球磨粉末和熱壓燒結(jié)參數(shù)下Nb-Si難熔合金的顯微組織演變和力學性能,分析了Nb-Si二元合金以及含合金化元素Ti、Fe合金的強韌化機制,考察了材料的高溫壓縮變形行為以及變形后的顯微組織。 對Nb-16Si二元和Nb-16Si-18Ti三元粉末系統(tǒng)機械合金化的研究結(jié)果表明無水乙醇用量、初始Nb粉末粒度以及Ti粉末的加入均影響球磨進程。球磨過程中,Nb顆粒經(jīng)塑性變形成片狀而后在加工硬化作用下逐漸細化成絮狀,Si逐漸固溶到Nb的晶格中形成過飽和固溶體。過量的無水乙醇推遲了球磨進程,而過長時間的球磨導致介質(zhì)污染的引入而形成富Fe的另一種鈮基固溶體。Ti的低密度使得同質(zhì)量的粉末體積較大,在相同的球磨參數(shù)下三元粉末系統(tǒng)的球磨進程明顯慢于二元粉末。 采用真空熱壓燒結(jié)法制備了Nb-16Si二元難熔合金,分析了燒結(jié)溫度、燒結(jié)時間和球磨粉末狀態(tài)對燒結(jié)材料的顯微組織演變及力學性能的影響。在1500°C下保溫60min得到了致密度超過99.2%的燒結(jié)材料,合金由Nbss、Nb3Si和Nb5Si3三相組成,大量孔隙導致低溫燒結(jié)材料的力學性能較差。隨球磨時間的延長熱壓燒結(jié)材料的顯微組織逐漸細化為平均顆粒尺寸僅2μm左右的近等軸狀,Nbss體積分數(shù)減少,大尺寸和高含量的韌性相能夠有效改善材料的室溫脆性,由此室溫斷裂韌性降低而彎曲強度增加。在1600°C下采用粉末鍛造技術(shù)一次成形了Nb-Si難熔合金推力室模擬件,零件具有良好的力學性能和與燒結(jié)材料相似的等軸狀組織,材料利用率高且成本低。 研究了合金化元素Ti、Fe對熱壓燒結(jié)Nb-Si難熔合金的顯微組織演變及力學性能的影響,探討了組織對性能的影響規(guī)律和材料的強韌化機制,考察了高溫壓縮行為及其變形后的組織。Fe的加入因合成Nb_4FeSi新相而使材料強度提高,但沒有改變組織形貌。含Ti的片狀復合粉末經(jīng)燒結(jié)后材料的顯微組織和性能呈各向異性,在垂直于和平行于熱壓方向的截面上Nbss分別為平行的條狀流線和雜亂的片狀。裂紋擴展路徑垂直于條狀Nbss時塑性變形以及裂紋橋聯(lián)和偏轉(zhuǎn)等有效提高了材料的斷裂韌性,其最高值超過16MPa·m~(1/2),彎曲斷口為撕裂棱和韌窩韌性斷裂特征,而Ti固溶到Nb中引起的強化使材料獲得較好的綜合力學性能。垂直于流線方向的高溫壓縮變形中,Nbss發(fā)生塑性壓縮且變形后條狀Nbss變細,韌性相尺寸影響壓縮塑性,而沿流線方向壓縮時,變形通過顆粒轉(zhuǎn)動和界面滑移帶動片狀Nbss向垂直于加載方向偏轉(zhuǎn)。
[Abstract]:The microstructure of the Nb-Si refractory alloy usually contains the base solid solution (Nbss) and the metal silicide (Nb _ 5Si _ 3/ Nb _ 3Si), and has the advantages of high melting point, low density and good high-temperature strength and the like, thus being a high-temperature structural material with great potential to meet the requirements of a new generation of aviation engine. However, the properties of the Nb-Si refractory alloy, such as the coarse and the component segregation of the Nb-Si refractory alloy, are influenced by the defects such as the coarse structure and the component segregation, and the intrinsic brittleness of the intermetallic compound also prevents the practical application of the Nb-Si refractory alloy as the high-temperature structural material. The Nb-Si binary refractory alloy and the Nb-Si multi-element refractory alloy (Si content 16at) with different Ti and Fe content were prepared by mechanical alloying and vacuum hot-press sintering.%) and the engine thrust chamber simulator is formed by a powder forging short flow technique, The microstructure evolution and mechanical properties of different mixed powder systems in mechanical alloying were studied. The microstructure and mechanical properties of Nb-Si refractory alloys under different conditions of ball milling and hot-pressing sintering were studied. The binary alloy of Nb-Si and the alloying elements Ti were analyzed. The toughening mechanism of Fe alloy is studied, and the high temperature compressive deformation behavior of the material and the microstructure after deformation are investigated. The results of the mechanical alloying of the Nb-16Si binary and Nb-16Si-18Ti ternary powder system show that the amount of absolute ethyl alcohol, the particle size of the initial Nb powder and the addition of the Ti powder influence the ball milling. in the process of ball milling, the Nb particles are plastically deformed into a sheet and then gradually refined into a flocculent under the action of the work hardening, and the Si is gradually dissolved into the crystal lattice of the Nb to form a supersaturated solid solution The excess amount of absolute ethyl alcohol has delayed the ball milling process, while over-time ball milling results in the introduction of media contamination to form a rich Fe-rich, one-based solid solution The bulk. Ti low density makes the powder volume of the same mass larger, and the ball milling process of the three-way powder system is obviously slower than that of the binary powder under the same ball milling parameters. In the end, Nb-16Si binary refractory alloy was prepared by vacuum hot-pressing and sintering, and the microstructure and mechanical properties of the sintered materials were analyzed. The sintering material with density of more than 99.2% is obtained at 1500 擄 C for 60min. The alloy is composed of three phases of Nbss, Nb3Si and Nb5Si3, and a large number of pores lead to the mechanical property of low-temperature sintered materials. the microstructure of the hot-pressed sintered material with the ball grinding time is gradually refined into a near equiaxed form with the average particle size of only about 2. m u.m, the volume fraction of the Nbss is reduced, the large-size and the high-content toughness phase can effectively improve the chamber of the material, the temperature is brittle, thus the fracture toughness of the room temperature is reduced and the bending strength is strong. Nb-Si refractory alloy thrust chamber simulation part is formed at a time of 1600 DEG C by a powder forging technology, the part has good mechanical property and the equiaxed structure similar to that of the sintered material, and the material utilization rate is high; The effects of alloying elements Ti and Fe on microstructure evolution and mechanical properties of hot-pressed sintered Nb-Si refractory alloys have been studied. The influence of the microstructure on the properties and the mechanism of strengthening and toughening of the materials are discussed. The high-temperature compression behavior and its change are also investigated. The addition of Fe increases the strength of the material due to the new phase of the synthesis of Nb _ 4FeSi, but has not changed. the microstructure and the property of the flaky composite powder containing Ti are anisotropic, and the Nbss in the cross-section perpendicular to and parallel to the hot-pressing direction is a parallel strip-shaped streamline and The crack propagation path is perpendicular to the strip-shaped Nbss, the plastic deformation and the crack bridge and the deflection can effectively improve the fracture toughness of the material, the maximum value of which is more than 16MPa 路 m ~ (1/ 2), and the bending fracture is the tearing edge and the tough-and-socket. The characteristics of the fracture characteristics, and the strengthening of Ti to the Nb causes the material to obtain a better harness. in the high-temperature compressive deformation perpendicular to the flow direction, the Nbss is plastically compressed and the deformed bar-shaped Nbss is thin, the size of the toughness phase influences the compression plasticity, and when compressed in the direction of the flow line, the deformation passes through the particle rotation and the interface slip to drive the flaky Nbss to be perpendicular to the addition
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：博士
【學位授予年份】：2011
【分類號】：TG132.32;TF124.3

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