Composition, nanostructure and origin of the ultrahardness in nc-TiN/a-Si3N4/a- and nc-TiSi2 nanocomposites with HV= 80 to ≥ 105 GPa
Composition, nanostructure and origin of the ultrahardness in nc-TiN/a-Si3N4/a- and nc-TiSi2 nanocomposites with HV= 80 to ≥ 105 GPa
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DOI：
10.1016/s0257-8972(00)00957-9
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发表时间：
2000-11
影响因子：
5.4
通讯作者：
S. Vepřek;A. Niederhofer;K. Moto;T. Bolom;H.-D. Männling;P. Nesládek;G. Dollinger;A. Bergmaier
中科院分区：
文献类型：
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作者：
S. Vepřek;A. Niederhofer;K. Moto;T. Bolom;H.-D. Männling;P. Nesládek;G. Dollinger;A. Bergmaier
采用等离子体化学气相沉积法在钢基体上制备了由纳米晶TiN、非晶Si_3N_4、非晶和纳米晶TiSi_2、nc-TiN/a-SiNx/a-和nc-TiSi_2组成的多相纳米复合涂层（3-20 μm）。通过施加30至200 mN载荷的载荷深度传感技术测量了80至>105 GPa的与载荷无关的维氏显微硬度，并通过使用SEM测量剩余塑性压痕的尺寸进行了验证。复杂分析的结果提供了晶界性质的一致图片，该晶界决定了硅含量在约3至22原子%之间的整个范围内的硬度。在≥ 2.5mA/cm ~ 2的高放电电流密度下，a-Si_3 N_4形成晶界，复合材料具有超硬（40-50 GPa）。在≤1 mA/cm ~ 2的较低电流密度下，形成TiSi_2和Si_3 N_4的混合物。随着Si含量的增加，TiN纳米晶晶界中的a-TiSi 2含量增加，并且在10 at.%以上在Si中析出约3 nm的TiSi 2纳米晶。Si_3N_4含量和TiSi_2/Si_3N_4比值对硬度的影响是复杂的。当TiN纳米晶表面覆盖有约一个单层的Si 3 N4时，实现了≥80 GPa的超硬度。在这些条件下，80-100 GPa的超硬度取决于α-和nc-TiSi 2的量。
Multiphase nanocomposite coatings (3–20 μm thick) consisting of nanocrystalline TiN, amorphous Si3N4, and amorphous and nanocrystalline TiSi2, nc-TiN/a-SiNx/a- and nc-TiSi2were deposited on steel substrates by means of plasma CVD. The load-independent Vickers microhardness from 80 to >105 GPa was measured by the load–depth sensing technique for applied loads between 30 and 200 mN and verified by measuring the size of the remaining plastic indentation using SEM. The results of a complex analysis provide a consistent picture of the nature of the grain boundaries which determines the hardness in the whole range of silicon content between approximately 3 and 22 at.%. At a high discharge current density of ≥2.5 mA/cm2the a-Si3N4forms the grain boundaries and the nanocomposites are superhard (40–50 GPa) as we reported earlier. At a lower current density of ≤1 mA/cm2a mixture of TiSi2and Si3N4is formed. With increasing Si-content the amount of a-TiSi2in the grain boundaries of the TiN nanocrystals increases, and above 10 at.% of Si approximately 3 nm small TiSi2nanocrystals precipitate. The hardness depends critically and in a complex way on the Si3N4content and the TiSi2/Si3N4ratio. The ultrahardness of ≥80 GPa is achieved when the surface of the TiN nanocrystals is covered with approximately one monolayer of Si3N4. Under these conditions the ultrahardness of 80–100 GPa depends on the amount of a- and nc-TiSi2.