| The ?deep prospecting’ is national strategy. The key method to implement this stratergy is developing the deep hole drilling diamond bits. The main problem of the new diamond bits is preparing the metal bond. In order to adapt the diamond bits’ development, more attention is paid to the pre-alloyed powders. Although the preparation and application of the pre-alloyed powders make a great progress, the microstructures of the powders and modification mechanisms need to be studie d more deeply. In addition, pressureless sintering are used widely in superhard materials manufacturing due to the advantages of simple operation, low production cost et al, but less researches are focused on the pressureless process and sintering mechanis ms.Considering the current research and application characters of the pre-alloyed powders, in this study, the Fe Co Cu pre-alloyed powders were prepared by co-precipitation method. The preparation technology and sintering characters were researched. The interface between the diamond and Fe Co Cu pre-alloyed powders was disscussed. The pressureless sintering process and the thermodynamic characters of the pre-alloyed powders was investigated. At last, the pre-alloyed powders formula systems were designed and the verification test were carried out. The main research results are as follows:(1)Based on the co-precipitation method, the Fe Co Cu pre-alloyed powders with different Fe-Cu ratio were prepared. The preparation technologies, sintering technologies and sintering characters were studied. The results showed that the optimal preparation parameters were the p H was 2.0, the reaction temperature was 50 ℃, the solution concentration was 1.0mol/L and the solution adding system was together drop method(when the concentration of the precipitant was 1.0mol/L). The intermetallic phases of Co3Fe7, Co Fe15.7 and Fe Cu4 are observed in all the three alloyed powders. The powders with lower Cu content had the finer particle size. The samples with higher Fe content had the better mechanical properties. The fracture SEM images of the matrix show that the samples with higher Cu content presented the diampe fracture and the higher Fe content samples presented the transgranular fracture.(2)The interface reaction between the diamond and the pre-alloyed powders were studied. The results show that the samples with higher Fe content had the better diamond holding strength.Co element had certain enrichment in the interface. The tests such as XRD, Raman, FTIR, TEM et al show th at graphitization was the main reaction at the diamond surface.(3)The pressureless sintering process of the three Fe Co Cu pre-alloyed powders’ cold pressure molding samples was studied systematically. The results show that all the three samples had an expansion stage before the shrinkage. The expansion ratio was larger with higher Cu content. For the same samples the lower heating rates mean that the higher densification degree. In the initial and final sintering stage the activation energy was fit for the Arrhenius curve, but in the middle stage the activation energy was affected by many factors. For the same samples at the lower heating rate, the activation energy was higher due to the longer retention stage.(4)The DSC curves of the three samples at diff erent heating rates show that all the three powders have endothermic process firstly, then turn into exothermic process with increasing of temperature. The DSC curves are sharper when heated at higher heating rate. With increasing of Fe content, the heat f low is larger. The specific heat capacity curves of the three samples are similar to the DSC curves. The higher heating rates correspond to the larger enthalpy. The activation energy in the expansion-shrinkage changing stage of the 25wt%Fe-15wt%Co-60wt%Cu is close to that of the 45wt%Fe-15wt%Co-40wt%Cu, but the activation energy of the 65wt%Fe-15wt%Co-20wt%Cu is 10 times higher than the first two specimens.(5)By designing the formulas for the medium to hard formation, the property differences of the Fe Co Cu pre-alloyed powders and the simple substance were discussed. The results show that the optimal mass fraction of every content in the condition of the pre-alloyed powders formula system was that: WC was 40wt%, 65wt%Fe-15wt%Co-20wt%Cu was 45wt%, Cu Sn15 was 7wt% and Ni was 8wt%. The mechanical data of the two formulas demonstrated that pre-alloyed powders could enhance the mechanical properties effectively. SEM and EDS results proved that pre-alloyed powders could avoid the segregation effectively, then the properties of the matrix would be inhenced. Based on the optimiazated diamond parameters, the drilling experiments were carried out. Results showed that the pre-alloyed powders could increase the drilling effect efficiently. |
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