Abstract: The technology of transient-liquid-phase(TLP) bonding of superalloy K18 and the behavior of its elements during the diffusion process had been studied.By applying this diffusion bonding technique (with isothermal solidification),the authors solved the problem of hot cracking in the fusion welding of cast Ni-base K18 high temperature alloy.The diffusion behavior of the elements,particularly boron,was carefully investigated.Autoradiographic and metallographic findings confirmed that boron in the form of M₃B₂ promoted the formation of σ-phase.The key to the successful bonding of K18 alloy was to control the diffusion of boron.Not until the later stage of the isothermal solidification diffusion bonding process did the diffusion of boron follow roughly Fick's law.TLP bonding helped a lot in joining difficult to weld high temperature alloys.It could be also considered as a potential means of making joints of dissimilar materials.