Chollon Georges, Langlais Francis, Placide Maud
Laboratoire des Composites Thermostructuraux (CNRS, SPS, CEA, UB1), University of Bordeaux, 3, allée de La Boétie, 33600 Pessac, France.
J Nanosci Nanotechnol. 2011 Sep;11(9):8333-6. doi: 10.1166/jnn.2011.5030.
Transient CVD experiments were simulated by varying continuously the deposition temperature or the initial gas flow rates (Q(MTS) or Q(H2)). Their consequences on the physicochemical properties of the coatings have been first examined. The adhesion of SiC/SiC bilayers containing these "transient interphases" (phi(Tr)) was investigated by scratch testing. For transient stages resulting from a decrease of Q(MTS) or T, free silicon can be co-deposited in proportions depending on alpha = Q(H2)/Q(MTS), T and P. This phenomenon is related to the high reactivity of the Si bearing species and is activated by high T and P and low a values. In this case, the continuous covalent bonding through the Si-rich interphases preserves the adhesion between the two SiC layers. Transient stages resulting from a decrease of Q(H2) lead first to larger and columnar SiC grains and finally to the deposition of anisotropic carbon, due to the formation of unsaturated hydrocarbons in the gas phase. The interphases with the highest carbon concentrations and thicknesses lead to delamination and local chipping of the outer SiC layer. The poor shear strength of these continuous and anisotropic layers is detrimental to the adherence of the bilayers.
通过连续改变沉积温度或初始气体流速（Q(MTS)或Q(H₂)）来模拟瞬态化学气相沉积实验。首先研究了它们对涂层物理化学性质的影响。通过划痕试验研究了含有这些“瞬态界面”（φ(Tr)）的SiC/SiC双层的附着力。对于由Q(MTS)或T降低导致的瞬态阶段，自由硅可以根据α = Q(H₂)/Q(MTS)、T和P的比例共沉积。这种现象与含硅物种的高反应性有关，并由高T和P以及低α值激活。在这种情况下，通过富硅界面的连续共价键保持了两个SiC层之间的附着力。由于气相中不饱和烃的形成，由Q(H₂)降低导致的瞬态阶段首先会导致更大且呈柱状的SiC晶粒，最终导致各向异性碳的沉积。具有最高碳浓度和厚度的界面会导致外层SiC层分层和局部剥落。这些连续且各向异性层的低剪切强度对双层的附着力不利。
