The present work was undertaken for better understanding of the basic processes involved in the recovering of carbides from sintered hard metals, and the interaction between Co-bonded tungsten carbide and molten zinc has been studied in the temperature range 480°-900°C. Techniques used for analyzing the obtained diffusion layers are EPMA, optical microscopy and X-ray diffraction.
The reaction layers are characterized by lamellar structures consisted of alternative WC and metal layers. The structure of the reaction layer and the interlamellar spacing are remarkably influenced by heating temperature and cooling condition but not by heating time. A tentative mechanism of the formation of lamellar structures has been proposed based on the experimental results.

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Sintering characteristics of TiN-TiC-Ni mixed powder compacts were studied by heating them in a gas atmosphere of nitrogen, hydrogen and argon, or in vacuum.
Shrinkage during sintering was disturbed by an abnormal expansion in a gas atmosphere of argon and hydrogen, or in vacuum, whereas in nitrogen the abnormal expansion was suppressed by the nitrogen pressure. So that the abnormal expansion is thought to be caused by the denitrification which took place during the formation of nitrocarbide, Ti(N, C).
Since the solubility in the nickel-solid solution increased with rise of the sintering temperature up to 1340°C, it may be considered that a eutectic between nickel-solid solution and Ti(N, C) occurs at about 1340°C.

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As a shrinkage of Ti(N, C)-30wt%Ni mixed powder compacts during sintering was remarkably promoted not only in vacuum, but also in argon, hydrogen and nitrogen atmosphere without an abnormal expansion, we concluded that the abnormal expansion during sintering of TiN-TiC-Ni mixed powder compacts¹⁾ was caused by denitrification which took place during the formation of Ti(N, C) solid solution.
Grain growth of sintered bodies was suppressed with an increase of nitrogen content of the nitrocarbide.
In sintering of TiN_x-TiC_y-30wt%Ni mixed powder compacts, the expansion was arrested; the composition showing the maximum sintered density in the sintering condition at 1500°C for 1 hr. was TiN_0.6-15wt%TiC-30wt%Ni.
Use of TiC_y powders also prevented the occurrence of the abnormal expansion during sintering.

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For the purpose of improving cutting properties of Ti(C, N) base cermet, the microstructure and several mechanical properties of TiC_0.7N_0.3-15Ni-8Mo alloy were investigated in relation to the change of additional carbon content. Moreover, in order to clarify the effect of additional carbon content and TiN addition on strengthening of the binder phase, the changes of Ti and Mo concentrations, hardness and lattice parameter of the binder phase of coarse grained TiC-(0, 5, 10, 20) TiN-30Ni-l5Mo alloys were investigated.
The results obtained are as follows;
(1) The growth of the intermediate phase formed around the core of the hard phase (TiC_0.7N_0.3) of TiC_0.7 N_0.3-15M-8Mo alloy in sintering process was not appreciably affected by the change of additional carbon content.
(2) The lattice parameter of the binder phase, hardness, transverse-rupture strength, compressive yield strength, and wear resistance in continuous cutting test in turning steel of TiC_0.7N_0.3-15Ni-8Mo alloy increased with decrease of additional cabon content.
(3) Ti concentration in the binder phase of coarse grained TiC-30Ni-15Mo alloy was as much as 4-8% depending on the additional carbon content. On the other hand, Mo concentration was much lower, i.e. 0.5-1.0wt%. Furthermore, Mo concentration in the binder phase of the alloy increased remarkably by the partially replacement of TiC with TiN. In contrast, Ti concentration in the binder phase decreased by 25%-50% with the addition of TiN, the rate of the decrease being smaller with the alloy of lower carbon content.
(4) The improvement of the mechanical and cutting properties of TiN bearing low carbon alloy was attributed to the effect of solid solution strengthening of the binder phase through greatly increased dissolution of Mo.

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TiB₂ must be used in a composite form having a high mechanical strength for use in application. When Ni4B3, (or NiB, or CoB) was added to TiB₂, they were found to compose a strong cermet. However, it is still not clear how the sintering conditions effect the mechanical properties of the alloys.
This paper describes, firstly, the effects of the sintering temperatures on the mechanical properties of TiB₂-8.8%Ni₄B₃, TiB₂-l1%NiB, TiB₂-11.3%CoB, and TiB₂-10.4%FeB sintered alloys; secondary, the effect of the sintering conditions such as the amount of binders and sintering time on those of TiB₂-NiB and TiB₂-Ni₄B₃ sintered alloys; finally, the additive effects of metal-diboride on the mechanical properties of compacts in the case of using a direct flow method of electric current. The results were as follows:
1. NiB is the best binder for TiB₂-binder alloys.
2. When a TiB₂-binder mixed powder sample is sintered and well compacted, TiB₂ grains grow markedly. Therefore, the transverse rupture strength of these alloys showed a marked decreased.
3. Additive metal-diborides restrain the growth of the TiB₂ grains with the following composites, TiB₂-5%VB₂-1%CoB, TiB₂-5%VB₂-1%FeB, TiB₂-5%NbB₂-1%NiB, TiB₂-5%NbB₂-1%CoB, TiB₂-5%NbB₂-1 %FeB, TiB₂-5%TaB₂-1%NiB, TiB₂-5%TaB₂-1%CoB, TiB₂-5%TaB₂-1%FeB, TiB₂-5%CrB₂-1%CoB, TiB₂-5%MoB₂-1%NiB and TiB₂-5%MoB₂-1%CoB. Therefore these compacts have a high transverse rupture strength and a high density. 4. These three component system sintered alloys have a Vickers hardness (300 g load) Hv of 900-1100 kg/mm² at 700°C.

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