The quality of this transition is best visualized by a straight line drawn between two circles: the line's only point of contact with each circle is tangential.
The contact between fluids is usually gradual rather than sharp, forming a transition zone of mixed fluid.
流体间的接触面常常是渐变的而不是突变的，形成一个混合液体的过渡带。
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This paper deals with the technique of laser cladding on contact surface of gears, micro hardness distribution, microstructure and properties of cladding and transition layer.