Fabrication and modification of Ni3Al intermetallic compound and evaluation of its joint properties by transient liquid phase method In this study, the effect of boron additive on the hardness and microstructure of Ni3Al was studied and And the optimum amount of boron was added to improve the structure of the Ni 3 Al intermetallic compound. Also, the jointing of Ni 3 Al intermetallic compound using transient liquid phase process was investigated.It was determined that the density of dendrites increases as a result of the addition of boron, and space between the secondary arm decreases due to the increase in constitutionally supercooling. The results of the Vickers hardness test showed that the specimen without a boron had 190 HV hardness and white adding boron to 2 at. % reached 352 HV. In the following, a transitional liquid phase method was used to jointing the Ni 3 Al intermetallic compound. In this study, joining was performed at vacuum furnace at 1050 C 0 and the effect of copper and AWS BNi-2 interlayer on the bonding region was investigated for four times at 30, 60, 90 and 120 minutes. The joint area was investigated by optical and Scanning Electron Microscope. Investigations showed that no Isothermally Solidifed Zone was formed at joining with the AWS BNi-2 interlayer for 120 minutes and only with increasing time, Brittle phases were reduced in Athermally Solidifed Zone at the Jointing. Energy Dispersive X-Ray Spectroscopy analysis on copper-bonded specimens showed that the Diffusion Affected Zon is formed at joints. Also, the results showed that up to 90 minutes Brittle phases still exist in Jointing, But by increasing the time to 120 minutes, a solid solution of copper was formed in the Jointing. The investigation of microstructure changes in different regions along the Jointing and around it showed that in jointing with the AWS BNi-2 interlayer, the highest hardness was formed in the central line of the joint so that with increasing time Up to 120 minutes, the hardness increases to 722 HV. The hardeness profile of jointing with Copper interlayer It was seen that hardness was increased by increasing the time to 90 minutes, and with increasing time to 120minutes, the hardness in the center line of joints decreased to 224 HV. The joints were draged by a tension device and a fixture, and the shear strength was measured. The results showed that in joints white AWS BNi-2 interlayer, the shear strength increased with increasing time, so that the shear strength increased to 217 MPa for 120 minutes. In joints white Copper interlayer, the highest shear strength was obtained 60 MPa at the time of 30 minutes due to the presence of a nickel-rich matrix. With increasing time for up to 90 minutes, the shear strength decreased and reached 34 MPa and at 120 minutes, shear strength increased again to 44 MPa due to the formation of a copper-rich solid solution and the elimination of eutectic compounds. Considering that the highest shear strength was related to the BNi-2 interlayer and the duration of 120 minutes, this interlayer and this time were selected as the best parameters, and applied on an optimum sample of% 1 Boron to investigate the effect of boron in the base metal on the binding properties. Studies have shown that under the influence of the presence of boron on the base metal and the decrease of Gradient concentration of this element, the amount of nickel and chromium boride and Ni 3 Si phase in the joint increased in comparison with the sample without boron at time of 120 minutes. This increased the hardness to 792 HV in the center line of the joint and reduced the shear strength to 203 MPa. Investigation of the fracture surface by the electron microscope showed that the joints with the AWS BNi-2 were all broken in brittle fracture mode. For the joints white copper interlayer until the 90 minute, brittle fracture mood was overcoming, but with increasing time to 120 minutes failure often occurred softly. In joint for the sample white 1 at.% boron and AWS BNi-2 inter layer at the time of 120 minute also was more brittle than the sample Without boron In the same condition, as the amount of boron and the formation of brittle phases in the joint has increased. Finally, in general, the amount of boron at.% 1 was the optimal amount at which the highest degree of hardness and flexibility was achieved. All joints was successful at all times and interlayers, but the AWS BNi-2 interlayer and the 120 minute duration showed better performance than the copper interlayer. Key Words Ni 3 Al Intermetallic composition, transitional liquid phase process, boron, interlayer, Athermally Solidification.