Microstructure and Mechanical Properties of In Situ Synthesized Metastable ß Titanium Alloy Composite from Low-Cost Elemental Powders.

The titanium matrix composite was produced through a hot compaction process at 1250 °C using the mixture of elemental powders with chemical composition of Ti-5Al-5Mo-5V-3Cr and 2 wt.% addition of boron carbide. The phase analysis via X-ray diffraction method was performed to confirm the occurrence of an in situ reaction between boron carbide and titanium. Then, the wide-ranging microstructural analysis was performed using optical microscopy as well as scanning electron microscopy along with energy-dispersive X-ray spectroscopy and electron backscatter diffraction. Based on this investigation, it was possible to describe the diffusion behavior during hot compaction and possible precipitation capabilities of TiC and TiB phases. Tensile and compression tests were conducted to determine the strength properties. The investigated composite has an ultimate tensile strength of about 910 ± 13 MPa with elongation of 10.9 ± 1.9% and compressive strength of 1744 ± 20 MPa with deformation of 10.5 ± 0.2%. Observation of the fracture surface allowed us to determine the dominant failure mechanism, which was crack propagation from the reaction layer surrounding remaining boron carbide particle, through the titanium alloy matrix. The study summarizes the process of producing an in situ titanium matrix composite from elemental powders and B4C additives and emphasizes the importance of element diffusion and reaction layer formation, which contributes to the strength properties of the material.

Processing and Characterization of ß Titanium Alloy Composite Using Power Metallurgy Approach.

The ß titanium alloy matrix composite was made from a mixture of elemental metal powders, including boron carbide. During the high-temperature sintering process, in situ synthesis took place as a result of the TiB and TiC reinforcing phases formed. The identification of these phases was confirmed by X-ray diffraction and microstructural analyses. The presence of unreacted B4C particles and the surrounding reaction layers allowed for the evaluation of diffusion kinetics of alloying elements using SEM and EDS analyses. The direction of diffusion of the alloying elements in the multicomponent titanium alloy and their influence on the in situ synthesis reaction taking place were determined. In addition, the relationship between the microstructural components, strengthening phases, and hardness was also determined. It was shown that in situ reinforcement of titanium alloy produced from a mixture of elemental powders with complex chemical composition is possible under the proposed conditions. Thus, it has been demonstrated that sufficiently high temperature and adequate holding time allows one to understand the kinetics of the synthesis of the strengthening phases, which have been shown to be controlled by the concentrations of alloying elements.

Application of the Strain Compensation Model and Processing Maps for Description of Hot Deformation Behavior of Metastable ß Titanium Alloy.

The flow behavior of metastable ß titanium alloy was investigated basing on isothermal hot compression tests performed on Gleeble 3800 thermomechanical simulator at near and above ß transus temperatures. The flow stress curves were obtained for deformation temperature range of 800-1100 °C and strain rate range of 0.01-100 s-1. The strain compensated constitutive model was developed using the Arrhenius-type equation. The high correlation coefficient (R) as well as low average absolute relative error (AARE) between the experimental and the calculated data confirmed a high accuracy of the developed model. The dynamic material modeling in combination with the Prasad stability criterion made it possible to generate processing maps for the investigated processing temperature, strain and strain rate ranges. The high material flow stability under investigated deformation conditions was revealed. The microstructural analysis provided additional information regarding the flow behavior and predominant deformation mechanism. It was found that dynamic recovery (DRV) was the main mechanism operating during the deformation of the investigated ß titanium alloy.

Evaluation of Hot Workability of Nickel-Based Superalloy Using Activation Energy Map and Processing Maps.

The stress-strain curves for nickel-based superalloy were obtained from isothermal hot compression tests at a wide range of deformation temperatures and strain rates. The material constants and deformation activation energy of the investigated superalloy were calculated. The accuracy of the constitutive equation describing the hot deformation behavior of this material was confirmed by the correlation coefficient for the linear regression. The distribution of deformation activation energy Q as a function of strain rate and temperature for nickel-based superalloy was presented. The processing maps were generated upon the basis of Prasad stability criterion for true strains ranging from 0.2 to 1 at the deformation temperatures range of 900-1150 °C, and strain rates range of 0.01-100 s-1. Based on the flow stress curves analysis, deformation activation energy map, and processing maps for different true strains, the undesirable and potentially favorable hot deformation parameters were determined. The microstructural observations confirmed the above optimization results for the hot workability of the investigated superalloy. Besides, the numerical simulation and industrial forging tests were performed in order to verify the obtained results.