Grass R N, Dietiker M, Solenthaler C, Spolenak R, Stark W J
Institute for Chemical and Bioengineering, ETH Zurich, CH-8093 Zurich, Switzerland. Materials Research Center, ETH Zurich, CH-8093 Zurich, Switzerland.
Nanotechnology. 2007 Jan 24;18(3):035703. doi: 10.1088/0957-4484/18/3/035703. Epub 2007 Jan 3.
Bulk nanocrystalline cobalt was prepared from reducing flame-spray-derived cobalt nanopowders exclusively in the face-centred cubic (fcc) modification. Compacts of approximately 60% density were obtained from uniaxial compression at room temperature and showed a strong resistance towards grain growth upon subsequent sintering to 90% relative density. The nanocrystalline structure remained stable well above 1000 degrees C and resulted in a pore-rich metal with about 10(15) nanovoids cm(-3). These sintered compacts displayed an up to three times higher bulk hardness if compared to conventional cobalt and local ductility as evidenced from scanning electron microscopy and nanoindentation. The strong grain-growth resistance and consequent increase in material hardness are discussed in respect of the presence of nanovoids, twin boundaries and material contamination.
块状纳米晶钴是由还原火焰喷雾法制备的钴纳米粉末仅以面心立方（fcc）结构改性而成。通过室温下单轴压缩获得了密度约为60%的压坯，随后烧结至相对密度90%时，其对晶粒生长具有很强的抗性。纳米晶结构在远高于1000℃的温度下仍保持稳定，形成了一种富含孔隙的金属，其纳米空洞密度约为10(15) cm(-3)。与传统钴相比，这些烧结压坯的体硬度提高了两倍，扫描电子显微镜和纳米压痕测试表明其具有局部延展性。从纳米空洞、孪晶界和材料污染的角度讨论了其对晶粒生长的强抗性以及由此导致的材料硬度增加的原因。
