【作者】 谢春晓；

【导师】 杨元政；

【作者基本信息】 广东工业大学 ， 材料加工工程， 2013， 博士

【摘要】 在已开发出的各类非晶合金体系中,Fe基非晶合金因其明显的成本优势和钢铁材料的广泛应用性,使其显示出十分重要的工程应用价值。为了获得良好的玻璃形成能力以及制备出大尺寸的Fe基非晶合金,通常在Fe基非晶合金中添加一种或一种以上的类金属元素(B、Si、C、P等)。但这些Fe基非晶合金都存在脆性极大的缺陷,如在压缩试验中几乎没有塑性变形能力,弹性变形能力也十分有限,对Fe基非晶合金薄带及块体的脆性研究表明其脆性与类金属元素的种类、含量及其分布密切相关。目前,有关不含类金属元素的全金属组元Fe基非晶合金还鲜有报道。本文中,在课题组同行前期的研究基础之上,综合运用Inoue经验准则、深共晶点准则、大原子团簇和相似元素替换法,结合合金相图,综合考虑原子尺寸效应、合金成分效应和非晶相与晶化相之间的竞争效应对合金非晶形成能力的作用,设计出不含类金属元素的新型全金属组元Fe基非晶合金成分,成功制备出了五元FeCoNiCrZr和FeCoMoCrZr非晶合金薄带。以XRD、DSC、SEM、AFM、VSM等为主要研究手段,对这两个全新的Fe基非晶合金体系进行非晶形成能力、热稳定性、晶化动力学、晶化析出相、磁性能以及变形断裂力学性能等方面的研究,希望能为制备出具有良好塑性变形能力或优异磁性能的全金属组元Fe基大块非晶合金打下的理论基础。主要试验结果和结论如下：1)成功制备了(Fe0.52Co0.48-xNix)73Cr17Zr10(x=0.06,0.18,0.30)非晶合金薄带,结果表明：随着Co/Ni比的增加,特征温度Tg、Tx、Tp均向高温区移动,过冷液相区△Tx先增大后减小；x=0.18时,合金(Fe0.52Co0.30Ni18)73Cr17Zr10具有最宽的△Tx (△Tx=41.5℃)。变温晶化行为表明：采用Kissinger法与Ozawa法的计算结果非常接近,且都呈现Eg> Ex> Ep的规律；随着Co/Ni比的增加,Ex呈先增大后减小的趋势且阶段晶化激活能Ec(X)最大值呈下降趋势,当x=0.18时,非晶合金最难晶化。随着晶化分数x的增加,3种合金的Ec(X)均逐渐增加至一个最大值而后逐渐减小直到晶化转变的完成。2)成功制备了(Fe0.58Co0.42)73Mo17-xCrxZr10(x=9,12,17)非晶合金薄带,结果表明：随着Cr/Mo比的增加,Tg、Tx、Tp均向低温区移动,而△Tx逐步缓慢增加；x=17时,合金(Fe0.58Co0.42)73Cr17Zr10具有最宽的△Tx (△Tx=37.2℃)。变温晶化行为表明：各非晶合金都呈现Ex>Ep≈Eg的规律；随着Cr/Mo比的增加,Ex和Ep都呈增大趋势且Ec(X)最大值也呈上升趋势,当Cr完全取代’Mo,即x=17时,非晶合金最难晶化。随着晶化分数x的增加,3种合金的Ec(x)也均逐渐增加至一个最大值而后逐渐减小直到晶化转变的完成。3)(Fe0.52Co0.3oNio.18)73Cr17Zr10非晶合金的变温晶化动力学研究表明：变温晶化过程可以分成前后二个阶段,前一阶段符合形核与核长大模型,后一阶段符合晶粒正常长大模型。等温晶化动力学研究表明：等温温度对晶化过程中的形核与核长大行为有显著影响,随着等温温度升高,晶核长大由受扩散控制转变为受界面控制。等温晶化激活能高于变温晶化激活能,这说明等温晶化阻力高于变温晶化；Ec(x)的计算表明等温晶化阻力越来越大,而变温晶化阻力越来越小。4)铸态FeCoNiCrZr系和FeCoMoCrZr系非晶合金的饱和磁化强度Ms较低。不同退火温度对非晶合金的析出相的种类及晶粒大小产生明显的影响,从而导致磁性能发生明显的变化。(Fe0.52Co0.48-xNix)73Cr17Zr10(x=0.18,0.30)非晶合金的晶化过程为：Am→α-Fe(Co)+Am→α-Fe(Co)+Cr2Ni3+Fe3Ni2+Cr2Zr+未知相。(Fe0.58Co0.42)73Mo5Cr12Zr10非晶合金的晶化过程为：Am→α-Fe(Co)+CrFe4+Fe23Zr6+Cr2Mo。(Fe0.58Co0.42)73Cr17Zr10非晶合金的晶化过程为：Am→α-Fe(Co)+Am’→α-Fe(Co)+CrFe4+Fe3Ni2+Cr2Zr+未知相。当退火温度Ti<Tg时,由于结构弛豫,内应力的释放,合金的Ms有所提高；当退火温度为Txi<Ti<Tpl时,由于铁磁性α-Fe(Co)相的析出,合金的Ms显著提升。当退火温度高于Tp1时,由于晶粒长大和第二相的析出,磁性能急剧恶化。(Fe0.58Co0.42)73Cr17Zr10(?)(?)晶合金在565℃退火能获得最好磁性能,其Ms=126.2emu/g。退火态非晶合金薄带的AFM观察表明：AFM图片所呈现的颗粒尺寸要比用Scherrer法测得的α-Fe(Co)纳米晶尺寸大得多,这是典型的包裹晶粒现象。5)本文制备的合金薄带中,形成非晶结构的薄带在弯曲试验中均表现为弯曲韧性。(Fe0.52Co0.3oNi0.18)73Cr17Zr10非晶合金弯曲断口的SEM形貌显示：断口侧面有大量的剪切台阶,断口表面均匀分布着大量密集的纹状花样,表明这是典型的韧性弯曲断裂行为。在低于Tg退火时,由于结构弛豫对合金内部的自由体积产生影响,合金发生韧-脆转变现象。6)(Fe0.52Co0.3oNi0.18)73Cr17Zr10非晶合金薄带的显微硬度随退火温度及退火时间的变化规律表明：显微硬度随退火温度的上升先降低再升高,后又降低；低温退火时随时间的延长先降低再升高；高温退火时随时间的延长一直升高并最终趋于平稳。显微硬度的这种变化规律反映了非晶合金内部的结构变化过程。7)(Fe0.52Co0.30Ni0.18)73Cr17Zr10非晶合金经维氏压痕变形后,合金自由变形区由相互交错的半圆形和放射状剪切带构成。压痕平均对角线长度D、压痕中心O到自由变形区边缘的距离R随着载荷P的增加而增大,且R/D与P无关。半圆形剪切带传递具有不连续性而放射状剪切带传递具有连续性,表明前者在变形中优先形成。放射状剪切带与半圆形剪切带的切线方向之间的夹角20在大约89-90°之间变动,剪切变形受控于最大剪切应力并近似遵循Von Mises屈服准则。8)(Fe0.52Co0.30Ni0.18)73Cr17Zr10(?)晶合金在拉伸应变速率2.0×10-3s-1下,断裂强度为1320MPa,弹性应变量为2.1%,宏观上没有经过任何塑性变形试样即发生“灾难性"断裂。断口表面上的大量纹状花样及其他类型的花样,表明在微观上出现了塑性变形特征,由于塑性变形局限于局域剪切带内,局域剪切带的快速扩展导致了合金的宏观脆性断裂。更多还原

【Abstract】 Among the eveloped amorphous alloy systems, Fe-based amorphous alloys which possess relatively low material cost and broad application of steel materials, have been considered to have an important value of engineering application. In order to obtain good glass forming ability(GFA) and then to prepare Fe-based amorphous alloys with larger size, usually one or more type of metalloid elements(B, Si, C, P and so on) have been added in Fe-based amorphous alloys. But all these Fe-based amorphous alloys show great brittleness, such as almost no plastic deformation in compression test, and their elastic deformation ability is also limited. Study on the brittleness of Fe-based amorphous alloy ribbons and bulks showed that their brittleness is closely related with types, content and distribution of metalloid elements. At present, Fe-based amorphous alloys without metalloid is rarely reported.In this dissertation, the chemical composition of Fe-based amorphous alloys without metalloid were designed by considering Inoue empirical criterion, binary deep eutectic rule, large atomic cluster and similar element substitution and FeCoNiCrZr and FeCoMoCrZr amorphous alloy ribbons were prepared successfully. The GFA, thermal stability, crystallization kinetics, precipitated phase, magnetic properties and mechanical properties of these two new Fe-based amorphous alloy systems were investigated by X-ray diffriction(XRD), differential scanning calorimetry(DSC), scanning electron microscopy(SEM), atomic force microscopy(AFM), vibrating sample magnetometer (VSM), It is expected to be able to lay the theoretical foundation for producing good plastic deformation ability or good magnetic properties of Fe-based bulk metallic glasses without metalloid. The main results and conclusions are as follows:1)(Fe0.52Co0.48-xNix)73Cr17Zr10(x=0.06,0.18,0.30) amorphous alloy ribbons were successfully prepared. With increasing the Co/Ni ratio, all the characteristic temperatures including onset of glass transition temperature(Tg)、onset of crystallization temperature (Tx、 peak of crystallization temperature(Tp) move towards to the higher temperature regions, the supercooled liquid region(△Tx) increases firstly, and then decreases. When x=0.18, amorphous alloy has the most wide△TX(△TX=41.5℃). The activation energies calculated by the Kissinger and Ozawa equations show good agreement, and all amorphous alloys have the same law: Eg> Ex> Ep. With increasing the Co/Ni ratio, the crystallization activation energy Ex increases firstly and then decreases, the maximum of local crystallization activation energies(Ec(x) decreases. When x=0.18, crystallization is the most difficult. With the increase of crystallization volume fraction(x), the Ec(x) of all amorphous alloys gradually increases to the maximum and then gradually decreases to the end of crystallization.2)(Feo.58Coo.42)73Mo17-xCrxZr10(x=9,12,17) amorphous alloy ribbons were successfully prepared. With increasing the Cr/Mo ratio, all the characteristic temperatures including Tg、 Tx、Tp move towards to the low temperature regions,△TX increases slowly. When x=17, amorphous alloy has the most wide△TX(△TX=41.5℃). All amorphous alloys have the same law:Ex> Eg≈Eg. With increasing the Cr/Mo ratio, Ex and Ep increases, the maximum of Ec(x) also increases. When x=17, crystallization is the most difficult. With the increase of crystallization volume fraction(x), the Ec(x) of all amorphous alloys were gradually increases to the maximum and then gradually decreased until the end of crystallization.3) Study on the non-isothermal crystallization kinetics of (Fe0.52Co0.30Nio.0.18)73C17Zr10amorphous alloy showed that the non-isothermal crystallization mechanism is composed of two processes, namely the nucleation-and-growth mode and normal grain growth kinetic law. The isothermal crystallization kinetics showed that the phase transformation mechanism depends on annealing temperature. As the isothermal annealing temperature increases, the nucleus growth mechanism changes from diffusion-controlled growth to interface-controlled growth. The calculated Ec(x) indicates that along with the crystallization evolution the isothermal crystallization becomes more difficult, whereas the non-isothermal crystallization becomes easier,4) The saturation magnetization(Ms) of FeCoNiCrZr and FeCoMoCrZr amorphous alloys at cast state are relatively low. The annealing temperature (Ti) pays an obvious effect on the type and grain size of precipitated phases in these alloys then cause the magnetic property to change significantly. The crystallization process of (Feo.52Coo.48-xNix)73Cri7Zr10(x=0.18,0.30) amorphous alloy is showed as Am→α-Fe(Co)+Am’→α-Fe(Co)+Cr2Ni3+Fe3Ni2+Cr2Zr+unknown phase. The crystallization process of (Feo.58Coo.42)73Mo5Cr12Zr10amorphous alloy is showed as Am→α-Fe(Co)+CrFe4+Fe23Zr6+Cr2Mo. The crystallization process of (Feo.58Co0.42)73Cr17Zr10amorphous alloy is showed as Am→α-Fe(Co)+Am’→a-Fe(Co)+CrFe4+Fe3Ni2+Cr2Zr+unknown phase. When Ti is lower than Tg, Ms increases slightly for all annealed amorphous ribbons as a result of relaxation of the internal stress of the as-quenched amorphous alloy. When Ti is in between Tx1and Tp1, the Ms significant increases due to the partial crystallization of amorphous precursors to create a homogeneous distribution of a-Fe(Co) nanocrystals within a residual amorphous matrix. When Ti is higher than Tp1, the Ms drops rapidly, which may be caused by the grain growth and the formation of paramagnetic phase.(Feo.58Coo.42)73Cr17Zr10amorphous alloy after annealed at565℃for40min has the best magnetic property(Ms=126.2emu/g). The results of AFM observation showed that in the annealed amorphous ribbons the grain size mesured from AFM graphs is much larger than that of the a-Fe(Co) nanocrystalline size caculated by Scherrer method, which is a typical phenomenon of coated grain.5) All the prepared amorphous ribbons show a certain tough in bending test. SEM graphs of bending fracture of (Feo.52Coo.3oNio.18)73Cr17Zr10amorphous ribbon showed that the fracture side has a great deal of shear steps and a larger number of vein patterns were distributed evenly on the fracture surface, which is a typical ductile fracture behaviour. When annealing temperature is blow Tg, due to the effect of structural relaxation on the amorphous alloy internal free volume, transition of ductile to brittle fracture was observed.6) The change of microhardness of (Fe0.52Co0.30Ni0.18)73Cr17Zr10amorphous ribbon with annealing temperature and annealing time was studied. The results show that the microhardness declines firstly, then rises and then declines with the rise of annealing temperature. In low-temperature annealing, the microhardness rises firstly, and then declines with the time, in high-temperature annealing, the microhardness rises all the time until to equilibrium. The variation of microhardness reflects the internal structural change of amorphous alloy.7) After vickers indentation deformation, the free deformation zone of (Feo.52Co0.30Ni0.18)73Cr17Zr10amorphous alloy consists of alternate semi-circular shear bands and radial shear bands. With the increasing load(P), the average indentation diagonal length(D) and the distance(R) from indentation center to free deformation edge increase, R/D is independent of P. The semi-circular shear bands transfer discontinuiousely, but the radial shear bands transfer continuitious, which indicates that the semi-circular shear bands form earlier than radial shear bands. The angle(20) between radial shear bands and the tangent direction of semi-circular shear bands change between about89～90°, which indicates that the shear deformation is controlled by the maximum shear stress and approximately follows the Von Mises yield criterion.8)(Fe0.52Co0.30Ni0.18)73Cr17Zr10amorphous ribbons under the tensile strain rate of2.0×10-3s-1show brittleness at room temperature, its tensile strength is1320MPa and elastic strain is about2.1%. A larger number of vein patterns and other type of patterns on the fracture surface show that plastic deformation occurs at microscopic. Due to the plastic deformation is confined to localized shear bands, the rapid expansion of local shear bands lead to brittle fracture of alloy at macroscopic.更多还原