Waldemar Ziaja

The effect of microstructure on the mechanical properties of two-phase titanium alloys

Abstract This paper presents the results of investigations of the microstructure and mechanical properties of two-phase α+β titanium alloys after different heat treatment. The influence of the morphology of lamellar microstructure and phase composition on the tensile properties and fracture toughness of the alloys was studied. Static tensile, hardness and fracture toughness tests and microstructure investigations were performed. It was noticed that the cooling rate from the β-phase range and ageing conditions had an effect on the microstructure parameters, volume fraction and chemical composition of the β-phase, and has a significant effect on the mechanical properties of the alloys tested.

Modelling of Grain Microstructure of IN-713C Castings

This paper provides an analysis of experimental research results and numerical simulation of grain microstructure of turbine blade castings made of the IN-713C nickel superalloy. The numerical simulation was carried out by applying the ProCAST program. The geometric description of model assemblies and three-dimensional ceramic mould enclosure was developed. The boundary conditions as well as the thermal and physical coefficients for alloy and ceramic shell mould were selected for simulation purposes. The parameters of nucleation law based on normal (Gaussian) distribution as well as the values of equation coefficients were established in order to determine the growth rate of dendrite tips for the IN-713C alloy, depending on the undercooling. The experimental verification of boundary conditions for numerical simulation was carried out by comparison with the results of temperature distribution measurements performed in the castings. The analysis of grain microstructure was conducted on the surface and cross-sections of castings. The forecasted grain microstructure was determined using the CAFE module (ProCAST software). The cast microstructure as well as the value of grain growth and nucleation coefficients, which were used for numerical simulation of solidification process, were experimentally verified.

Influence of silicon carbide chills on solidification process and shrinkage porosity of castings made of nickel based superalloys

Abstract The paper presents the manufacturing methodology of IN713C castings by application of investment casting method and silicon carbide (SiC) chills. On the basis of numerical simulation and conducted microstructure analysis, it was established that the application of SiC chills results in significant decrease in shrinkage porosity, in comparison to castings without chills. The temperature measurement was carried out, and the influence of chills on the kinetics of solidification process was established. It was determined that the application of SiC chills causes the increase in cooling rate (∼0·1 K s−1), in comparison to the casting without chills. The authors carried out numerical optimisation with the use of ProCAST software and established which parameters have the largest influence on the solidification process of castings with and without chills. In addition to SiC, the graphite and Al2O3 were analysed as chill material in terms of influence on the predicted kinetics of cooling process and the shrinkage porosity of castings. The conditions of solidification process for castings, which are equipped with chills and are free from shrinkage porosity, were determined on the basis of obtained results.

Phase Transformations and Characterization of α + β Titanium Alloys

Phase transformations the effects of which are used in manufacturing processes of structural elements made of two-phase titanium alloys are discussed in the chapter. In order to describe the effect of microstructure on mechanical properties of titanium alloys, phase constituents of microstructure and possible phase compositions too were characterized. Authors presented methods of developing of microstructure and analyzed factors determining technological properties of titanium alloys, like hot plasticity (including superplasticity).

Thermo-Chemical Process of Aluminizing of the Nickel-Base Superalloy

The thermo-chemical treatment routes for Renè77 superalloy were developed comprising low activity and high activity aluminizing by CVD method. The influence of the treatment on the oxidation resistance in air and creep resistance of the alloy was examined. The cyclic oxidation tests at 1100°C for 500 cycles were carried out. Creep tests were performed at 982°C at the stress level of 124 and 151.7MPa. The chemical and phase composition of the surface layer was analyzed after aluminizing. It was found that aluminide coating enhanced oxidation resistance of the Renè77 superalloy without deterioration of its mechanical properties.

Dynamic fragmentation and spheroidization of α phase grains during hot deformation of Ti-6Al-4V alloy: Paper presented at the “XIII Scientific Conference on Titanium and Titanium Alloys 2017”, 24–27 September 2017, Janów Podlaski, Poland

Abstract Development of mechanical properties of titanium alloys is usually achieved by the control of their microstructure (globular, lamellar, bimodal). Dynamic fragmentation and spheroidization of elongated α phase grains, formed from martensite laths, in the microstructure of Ti-6Al-4V alloy are considered in the paper. The effects of α phase grain spheroidization was evaluated in tensile tests over a temperature range of 800–900°C and strain rate range of 10−3–10−2 s−1. Completed spheroidization of elongated α phase grains and subsequent growth of equiaxed grains for all deformation modes were found. A low value of apparent activation energy for deformation was calculated – suggesting grain boundary sliding was the main deformation mechanism. The results showed good correlation with the kinetic rate equation based on the Zener–Hollomon parameter.

Protective Coatings on Steel Dies for Wax Injection Process

Protective coatings are used today in many applications for reducing friction and wear of tools in hot-working process e.g. metal die casting, hot forging, metal die plastics injection. The main goal of undertaken investigation was to evaluate usability of those coatings for improving wear resistance of metal die applied in investment casting process for wax injection. The (Ti,Al)N and (Al,Cr)N PVD coatings were deposited onto X37CrMoV5-1 hot-work tool steel and their mechanical and tribological properties are characterized in the paper. Based on the results of microscope examinations, scratch test, hardness measurement the similar properties of (Ti,Al)N and (Al,Cr)N coatings were found. Moreover it was established that type of steel surface machining before coating deposition, i.e. grinding, electrical discharge machining (EDM) and milling, did not affect coating properties. Thin coatings replicate steel base roughness parameters as Ra, Rz and Rmax with over 95% of correlation. Based on tensile test results of wax/coated steel samples and wax/uncoated steel samples the lowest wax adhesion to (Ti,Al)N coating was confirmed.

The Role of Martensitic Transformation in Thermomechanical Development of Microstructure and Plasticity of Two-Phase Ti-6Al-4V Titanium Alloy

Phase constituent morphology in microstructure of two-phase α+β titanium alloys is determined by conditions of thermomechanical processing consisting of sequential heat treatment and plastic deformation operations. Results of previous research indicate that particularly solution treatment preceding plastic deformation significantly changes α-phase morphology and determines hot plasticity of titanium alloys. In the paper thermomechanical processing composed of β solution treatment and following hot forging of Ti-6Al-4V titanium alloy was analysed. Development of martensite plates during heating up and hot deformation was evaluated. Microscopic examinations revealed that elongated and deformed α-phase grains were fragmented and transformed into globular ones. Significant influence of martensitic transformation on elongation coefficient of α-phase grains after plastic deformation was confirmed. Based on results of elevated temperature tensile tests it was established that α-phase morphology in examined two-phase α+β titanium alloy, developed in the thermomechanical processing, can enhance their hot plasticity – especially in the range of low strain rates.

The Effect of Heat Treatment on Static and Dynamic Mechanical Properties of Rapidly Solidified and Plastically Consolidated RS442 Aluminium Alloy

Ultra-fine grained metallic materials are characterized by higher mechanical properties comparing with their conventional equivalents. However increase in strength under static load is not always accompanied by improved fatigue behaviour. Previous investigations on submicrocrystalline RS442 aluminium alloy produced by plastic consolidation of rapidly solidified flakes in the extrusion process revealed increase in its high cycle fatigue bending strength caused by annealing at 450°C. The aim of present studies was to evaluate the influence of heat treatment – also precipitation hardening – on static mechanical properties (hardness, tensile and yield strength) and fatigue strength of the alloy determined in high cycle stress controlled bending tests. Correlation between microstructure, static mechanical properties and fatigue behaviour was analyzed too.

Influence of Process Parameters on Cooling Conditions in Nickel Base Superalloy Investment Casting

The published results of the research on crystallization process of nickel base superalloy castings rarely take into account the effect of the wall thickness of the casting. Current study presents a comprehensive assessment of the impact of molten alloy temperature, mould temperature, mould thermal insulation and casting diameter on crystallization process of polycrystalline nickel base superalloy. Research was designed and conducted as an factorial experiment at two levels. Different diameter samples were designed and optimised by the numerical simulation of solidification process using ProCAST software. Inconel 713C nickel based superalloy was cast into alumina-silicate moulds produced by lost wax technique. Casting temperature during solidification was measured using thermocouples installed in sections having a diameter of 10 and 20 mm. Statistical analysis of the influence of the main process parameters and casting diameter on cooling rate, total freezing temperature range and critical temperature range was performed. Cooling rates in the range from 0.21 to 1.24°C/s were obtained. It was found that diameter of the casting, mould temperature and the thermal insulation of the mould had significant effect on the cooling rate.