【作者】 李晓；

【导师】 赫晓东；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2008， 博士

【摘要】 高硅钢具有优异的软磁性能,如中高频铁损低,磁导率高,矫顽力小,磁滞伸缩接近于零等。而且,高硅钢的厚度对磁性能有非常大的影响,厚度越薄高频铁损就越低。高硅钢特别适合应用于高频高速电机、中高频变压器和电抗器等。但由于高硅硅钢的塑性加工性能很差,极大地限制了它的应用。高硅钢箔(一般指厚度为0.02～0.2mm的板材)的制备工艺方法已成为本领域的一个重要的研究热点。目前,高硅钢箔制备工艺研究领域关注的热点主要有快凝法、特殊轧制法和CVD法等,其中只有CVD法制备品的质量可以被接受,但由于CVD也存在设备维护及环境污染等难以解决的问题而严重制约其大范围应用。电子束物理气相沉积工艺具有沉积速率高、无污染且易于制备厚度从数十微米到数百微米箔的特点,可望能够成为一种制备高硅钢箔的理想工艺方法。本文就此开展了相关研究,并获得了令人鼓舞的研究结果。最终获得的高硅钢箔厚度为64μm,密度为7.5 g/cm3,饱和磁化强度为1.88T,矫顽力最小值为1.89Oe,铁损P1/10k最小值为8.2 W/kg,为0.1mm取向硅钢同条件下铁损的45.6%,P0.5/20k和最小值5.2 W/kg,为0.1mm取向硅钢同条件下铁损的37.1%。通过试验研究和理论分析表明,以Fe-6.5wt.%Si单源EB-PVD工艺不能制备出高硅钢箔;而采用Fe-Si双源EB-PVD工艺可以制备出高硅钢箔;而且制备时,靶基距越高,硅钢箔中硅含量越低;在本试验条件下,只有当靶基距小于等于415 mm时才可以制备出高硅钢箔。EB-PVD制备态高硅钢箔密度为7.26g/cm3,是其理论密度的97%,电阻率为90μ?·cm,高于理论值82μ?·cm,而饱和磁化强度为1.73T,低于理论值1.8T。这说明制备态硅钢箔电磁性能较好,但仍需进行后处理改善。采用XRD、EDS、SEM和M?ssbauer等手段对制备的高硅钢箔组织形貌和结构进行了分析表征。研究发现:静止基板下获得的高硅钢箔靠近基板侧、中间部位和背离基板侧存在不同有序度、织构度的Fe(Si)固溶体和形貌组织。靠近基板侧高硅钢箔由无择优取向的无序固溶体A2组成,而中间部位和背离基板侧高硅钢箔都由存在明显(100)择优取向的有序固溶体B2组成,且背离基板侧高硅钢箔的(100)择优取向程度比中间部位高。高硅钢箔截面由靠近基板侧的细小等轴晶和从靠近基板侧到背离基板侧直径逐渐增加的柱状晶组成,其中背离基板侧处柱状晶的平均直径为25~50μm。同样,旋转基板下制备的高硅钢箔两侧Fe(Si)固溶体有序度、织构程度和截面形貌也不同。靠近基板侧由无择优取向的有序相DO3组成,而背离基板侧由含有弱(110)择优取向的有序相B2组成。高硅钢箔截面的组织由等轴晶-柱状晶-等轴晶-柱状晶组成,且柱状晶的直径离基板侧越远而越大,在背离基板处柱状晶的直径达到2~3μm。通过逐层分析制备态硅钢箔的相组成和形貌变化,提出了电子束物理气相沉积过程中高硅钢薄箔的生长机理,即无规形核-竞争生长。开始沉积时蒸气原子在基板上随机形核,形成的晶粒为无择优取向的细小等轴晶;随着沉积过程的继续,有些特殊位相的晶粒易于生长而被保留下来,形成的晶粒为柱状晶,且直径越来越大,织构度越来越明显。通过试验研究表明,高温快速退火工艺不但不能使高硅钢箔的密度增加,反而导致其致密度下降,出现了几乎垂直于试样表面的柱柱状晶间的“一”字形孔和平行于试样表面的等轴晶和柱状晶界面处的“一”字形孔。相反,热压处理能使高硅钢箔致密化。压强从30MPa增加到60MPa,硅钢箔的密度从7.2 g/cm3增加到7.5 g/cm3,饱和磁化强度由1.74T增加到1.88T。真空退火能明显改善高硅钢箔的软磁性能,矫顽力Hc由6.87Oe降低至最小值1.89Oe,剩磁MR由593G减小到最小值132G。更多还原

【Abstract】 High Si steel has excellent magnetic properties, such as low core loss in medium and high frequency, high permeability, low coercive force and almost zero magnetostriction. Also, the core loss is lower when the thickness is smaller. It is especially suitable for application in the high frequency and high speed electric machine, medium and high frequency transformer and reactor. But its poor ductility hinders its preparation and application. Therefore, preparation of high Si steel foil becomes a critical issue. Now, the preparation method mainly includes rapidly solidified method, special rolling method and CVD, etc. Except CVD process, fabrication and commercial scale production of high Si steel foil can not be developed due to various problems. And the CVD method has its own shortcoming, such as high repair rate and environmental pollution due to the application of a corrosive and poisonous gas SiCl4.Electron beam vapor deposition has a lot of merits, such as high deposition rate, pollution free and being easy to produce foil with from several tens to several hundreds microns and it is expected to be a good method for the preparation. Therefore, we did many researches on the preparation by EB-PVD and got some exciting results.The thickness and the density of the finally obtained high Si steel foil are 64μm and 7.5g/cm3, respectively. The coercive force is 1.89Oe and saturation magnetization is 1.88T. The minimum core loss P1/10k is 8.2W/kg, 45.6% of the loss of the 0.1mm thick grain oriented steel foil and the minimum core loss P0.5/20k is 5.2W/kg, 37.1% of the core loss of the 0.1mm thick grain oriented steel foil.Experimental results and theoretical analysis showed that high Si steel foil can’t be prepared by one source method using Fe-6.5 wt. % Si source since the Si atom oxidized actively in the vacuum chamber. While high Si steel foil can be obtained by two source method. The silicon content of steel foil decreased when the target-substrate distance was lower and high Si steel foil can be manufactured when the target-substrate distance was smaller than 415 millimeters in some conditions. The density of the high Si steel foil was 7.26 g/cm3, 97 percent of theoretical values, the electrical resistivity was 90μ?·cm, larger than theoretical one 82μ?·cm. And the saturation magnetization was 1.73T, smaller than theoretical value 1.88T. This indicated that that the electrical and magnetic properties were comparatively good and still required to being enhanced by increase of the densification.XRD,EDS,SEM and M?ssbauer spectroscopy were used to characterized and analyzed the high Si steel foil. It was found that: The as-deposited high Si steel foil from static substrate had different phase composition and microstructures on the side close to the substrate, middle place and the site far from the substrate. The high Si steel foil was composed of A2 phase with no texture on the side close to the substrate while the steel foil in the middle and on the side far form the substrate consisted of an ordering phase B2 with strong (100) texture. It was composed of small equiaxed crystal and columnar crystallite, the diameter of which was larger when it is more far from the side close to the substrate. The width of columnar grain size was 25~50μm on the side far from the substrate. Similarly, the high Si steel foil from a rotated substrate had different microstructures and phase compositions. It was composed of an ordering phase DO3 with no texture while it consisted an ordering phase B2 with weak (110) preferential orientation. It was composed of equiaxed crystal-columnar grain-equiaxed crystal-columnar grain. The width of the columnar grain grew larger when it was closer to the side far from the substrate and the width was 2~3μm on the side far from the substrate.In the evaporation-deposition process, the growth of high Si steel foil obeys the mechanism“random nucleation-preferential growth”. In other words, the evaporated atoms nucleate randomly at the beginning on the substrate. As a result, the formed grains are small equiaxed crystals. With the continual deposition, some grains with a special orientation are reserved due to being easy to grow. As a consequence, the width of columnar crystal grew larger and the texture degree enhanced.Experimental Research showed that high temperature rapid annealing can not improve the density and decreased a little on the contrary. Stick-like pores almost perpendicular to the surface of the Si steel foil were formed between the columnar grains and other stick-like pores parallel to the surface of the foil appeared in the interface between equiaxed grains and columnar grains. On the contrary, the hot pressure process can improve the densification degree of high Si steel foil. The density was improved from 7.2 g/cm3 to 7.5 g/cm3 and the saturation magnetization was enhanced from 1.74T to 1.88T as the pressure increased form 0MPa to 60MPa. In addition, vacuum annealing can improve soft magnetic properties markedly. Coercive force and remnant magnetism decreased from 6.87Oe and 593G to the minimum 1.89Oe and 132G, respectively.更多还原