Blade Castings Research Articles

Optimization of the composition of the foundry heat-resistant nickel alloy for the manufacture of cast working blades using the method of (mono) crystallization for promising gas turbines

Purpose. Development of the composition of a heat-resistant nickel alloy not containing rhenium for the manufacture of cast working blades by the method of directional (mono) crystallization. The alloy should have increased structural stability, while maintaining the level of mechanical, anti-corrosion and heat-resistant properties and a significant reduction in cost.Research methods. To estimate the structural and phase stability of high-temperature nickel alloys, various calculation methods were used: « ΔE-method» for assessing the balance of the chemical composition of the alloys by the value of the unbalance parameter of the doping system; PHACOMP and New PHACOMP – on the chemical composition of γ- solid solutions; developed in ZNTU complex methodology that establishes the relationship between the various parameters of structural stability.Results. Computing-analytical methods have been used to develop the composition of an economically-alloyed heat-resistant nickel alloy for the manufacture of cast blades by the method of directional (mono) crystallization, which does not contain expensive imported rhenium.Scientific novelty. Using computational and analytical methods, a composition of a heat-resistant nickel alloy with increased structural stability, resistance to high-temperature corrosion, and heat-resistant properties necessary for cast single-crystal products has been developed.Improvement of structural stability and improvement of the complex of properties of the developed alloy is provided by balanced doping with tantalum and tungsten (8.5 % at an average level), at reducing the content of carbon, molybdenum and cobalt by almost 2 times, and absence of the most expensive component in the composition – rhenium.Practical value. The developed economically-alloyed heat-resistant nickel alloy, which does not contain expensive rhenium, provides all the necessary operational properties, with a significant reduction in cost, and can be recommended for use in the manufacture of single-crystal cast blades of land-based gas turbine units.

Investigation of Fused Alumina Based-Mold Facecoats for DZ22B Directionally Solidified Blades.

The interaction between alloy melt and mold facecoats is the main factor affecting the surface quality of investment casting nickel-based superalloys. An investigation was undertaken to develop suitable refractories as facecoat materials for the directionally solidified blades of DZ22B nickel-based superalloys in order to avoid a sand-burning defect. The wettability and interface reactions between alloy melt and various facecoats were studied by using a sessile drop experiment and the real investment casting method, respectively. The results show that by adding Cr2O3 powder with the amounts of 2 wt.%, 5 wt.% and 10 wt.% in the fused alumina-based facecoats, the wetting angles between the alloy melt and facecoats decreased from 105.40° to 100.37°, 99.96° and 98.11°, respectively, while the sand-burning defect on the casting blade surfaces still formed during the process of directional solidification. However, by adding h-BN powder in the fused alumina-based facecoats, the wetting angles between the alloy melt and facecoats dramatically increased, the sand-burning defect on the casting blade surfaces was effectively inhibited and a metallic luster on the directionally solidified blades could be obviously observed. In this study, the suitable composition of mold facecoats for the investment casting of blades is 2 wt.% h-BN added fused alumina.

Influence of Manufacture Process Parameters on Dimensional Stability of Small Blade Castings

The production of precise castings by investment casting becomes an increasingly important manufacturing technology and many of isues of this method have to be addressed. This paper deals with evaluation of critical points on wax patterns of small blades. After the casting of certain product, the casting had a deviation from the required dimension. Investigation revealed that the effect on the resulting dimensional deviation is not only the casting process but also the wax pattern injection process itself. The engine and turbine blades are one of the most important parts in turbine or aircraft engine machinery. Casting deformation is an important feature of evaluation the quality of the turbine blade. In order to control the deformation of the turbine blade during investment casting, a novel compensation method based on reverse deformation was proposed in this study. The article investigates and evaluates critical points for deformation of the blades after their production on wax-press machine. In addition, the effect of the pre-deformation preparation and the human factor influencing effect during assembly is evaluated with the main aspect of not machining all surface of small blades.

Predicting the volume shrinkage while manufacturing the GTE turbine blades

The process analysis of manufacturing the castings of turbine moving blades demonstrated that approximately 5% of the blade blanks from a lot are rejected to a considerable geometric distortion of the blade airfoil. The turbine moving blade casting manufactured by the casting method with directed crystallizing may differ in its geometric and dimensional-accuracy parameters from the design model. The casting geometry varies as a result of high temperature and structural shrinkage deformations which are manifested as the hindered volumetric shrinkage and contraction during crystallizing and upon the casting knockout from the ceramic mould. High-temperature deformations may result in contraction of the casting mould and ceramic core shaping the inner blade cooling channels. As a result, to obtain the blade of the geometric form as set by the designer, it becomes necessary to predict the stress-deformed state of the moving blade casting in order to consider the volumetric shrinkage and deformation in advance. Therefore, predicting and considering the total volumetric shrinkage during the manufacture of the moving blade castings ensuring the minimum contraction of the process system “ceramic mould – casting – ceramic core” is a relevant problem for the modern blank production.

Study of single crystal turbine blades made of ZhS32 alloy with a promising scheme of cooling

The results of studying single-crystal turbine blades with a promising scheme of cooling, cast from a heat-resistant ZhS32 alloy using ceramic rods with high-temperature sintering additives and additional impregnation with a varnish solution are presented. The program of crystallizing blades with a single-crystal structure is improved on a VIP-NK installation. A comparison of the operation modes of the updated program and serial technology is presented. A pilot batch of blade castings is obtained under production conditions of a machine-building enterprise with an output suitable in single-crystal structure of about 94%. Blade castings are studied using X-ray diffraction, X-ray and ultrasound methods. Quantitative metallographic analysis is carried out on an optical complex to determine spacing between axes of the first order dendrites (λ1) of the alloy and the volume fraction of the micropores in the cross section of the pen and casting lock. The results of scanning electron microscopy study of macro-and microstructure of the blade castings with a promising cooling scheme showed that the structure is typical for ZhS32alloy in the cast state and is well formed in the elements of the inner cavity of monocrystalline blades.

Corrosion- and Hydrogen-Resistance of Heat-Resistant Blade Nickel-Cobalt Alloys

We study the influence of gas-turbine fuel ash and gaseous hydrogen on the mass losses caused by longterm corrosion and the mechanical properties of heat-resistant CM-88U-VI, CM-90-VI, and CM-104-VI cast blade materials. It is shown that the level of sulfide-oxide corrosion resistance of the investigated alloys (CM-104-VI > CM-90-VI > CM-88U-VI) correlates with the chromium content. The highest resistance (among similar materials) is exhibited by CM-104-VI alloy, especially for long-term hightemperature tests. The CM-90-VI single-crystal alloy proves to be least sensitive to the action of hydrogen in short-term tensile tests carried out within the temperature range 20–900°C under a pressure of 30 MPa.

Features of the single crystal structure of the turbine blades made of carbon-free and carbon-containing nickel superalloys

A comparative study of structural features of the blade castings having a single-crystal structure and made of heat-resistant carbon-free and carbon-containing high-temperature nickel alloys upon directional crystallization with 001 crystallographic orientation is carried out. The results of the effect of directional crystallization modes on the formation of the structure and defects of castings of working blades made of carbon-containing and carbon-free high-temperature nickel alloys are presented. Changes in the degree of pickling of the near-surface layer of casting are presented as a function of pickling conditions. The microstructure of the near-surface zone of castings made of ZhS32 heat-resistant alloy is studied after different modes of their technological processing. It is shown that blade castings with a single-crystal structure made of heat-resistant carbon-free superalloys have a tendency to formation of the block structure and appearance of surface recrystallized grains. Recommendations on the use of methods of nondestructive X-ray control of blades made of carbon-frees alloys and precautions regarding birth of microporosity on the shelf and in the blade lock are specified.

Influence of Heat Treatment on Defect Structures in Single-Crystalline Blade Roots Studied by X-ray Topography and Positron Annihilation Lifetime Spectroscopy

Single-crystalline superalloy CMSX-4 is studied in the as-cast state and after heat treatment, with material being taken from turbine blade castings. The effect of the heat treatment on the defect structure of the root area near the selector/root connection is emphasized. Multiscale analysis is performed to correlate results obtained by X-ray topography and positron annihilation lifetime spectroscopy (PALS). Electron microscopy observations were also carried out to characterize the inhomogeneity in dendritic structure. The X-ray topography was used to compare defects of the misorientation nature, occurring in as-cast and treated states. The type and concentration of defects before and after heat treatment in different root areas were determined using the PALS method, which enables voids, mono-vacancies, and dislocations to be taken into account. In this way, differences in the concentration of defects caused by heat treatment are rationalized.

Influence of gibbosity on recrystallization behavior of single crystal blade casting

Recrystallization (RX) defects formed in the gibbosities induced by platinum chaplet pins were studied by experiments and simulations for single crystal (SX) blade castings. Recrystallization occurs in 39 of the 80 gibbosities and can penetrate more than 250 μm into the SX blade. The RX occurrence ratios for the gibbosities in the upper, middle and lower positions of the blade are 83%, 50%, and 8% respectively, indicating a strong sensitivity of RX to the location height of the gibbosity. The microstructure is SX without the presence of micro misoriented grains in the cross-section of gibbosity of as-cast sample. Secondary carbide particles are found at the interface between the RX and SX grains. A composite image of backscattered electron (BE) and electron backscatter diffraction (EBSD) shows that the migration of the RX interface is hindered by coarse eutectic particles. A thermal elastoplastic model that considers the anisotropic mechanical properties of SX superalloys and is coupled with a finite-element method (FEM) was utilized to predict the deformation behavior during directional solidification. The FEM results reveal that the equivalent plastic strain (PEEQ) tends to concentrate in the gibbosities, and this gives a reasonable and reliable explanation for RX formation.

Effect of fine alumina in improving refractoriness of ceramic shell moulds used for aeronautical grade Ni-base superalloy castings

This paper discusses an improvement in shell refractoriness and dimensional stability of columnar grained (CG) low pressure turbine blade castings made using Ni base superalloy by directional solidification process (DS). Two ceramic shell systems were adopted, namely shell system I and II. Shell moulds were prepared by using ceramic slurries containing zircon flour as a filler material and colloidal silica as a binder. As compared to shell system II (zircon filler with colloidal silica binder and fine alumina), shell system I (zircon filler with colloidal silica binder) showed lower refractoriness. Shell system II showed an increase in the flexural strength both in the green as well as in fired conditions. Shells made from shell system II showed about 13% higher green strength and 55% higher fired strength as compared to shell system I. Shell system II also exhibited superior self sag resistance up to 1625 °C. Moulds prepared from this shell system yielded aeronautical grade casting with high dimensional accuracy even at a metal pouring temperature of 1550 °C. Moulds from shell system I, on the other hand, underwent sagging even at metal pouring temperature of 1500 °C, leading to dimensionally unacceptable castings. The superior performance of shells prepared from shell system II can be ascribed to the presence of fine alumina in the shell.

Prospects for the domestic production of large-sized cast blades and vanes for industrial gas turbines

Russian experience in the production of large-sized cast blades and vanes for industrial gas turbines is analyzed for the past decades. It is noted that the production of small- and medium-sized blades and vanes made of Russian alloys using technologies for aviation, marine, and gas-pumping turbines cannot be scaled for industrial gas turbines. It is shown that, in order to provide manufacturability under large-scale casting from domestic nickel alloys, it is necessary to solve complex problems in changing their chemical composition, to develop new casting technologies and to optimize the heat treatment modes. An experience of PAO NPO Saturn in manufacturing the blades and vanes made of ChS88U-VI and IN738-LC foundry nickel alloys for the turbines of the GTE-110 gas turbine unit is considered in detail. Potentialities for achieving adopted target parameters for the mechanical properties of working blades cast from ChS88UM-VI modified alloy are established. For the blades made of IN738-LC alloy manufactured using the existing foundry technology, a complete compliance with the requirements of normative and technical documentation has been established. Currently, in Russia, the basis of the fleet of gas turbine plants is composed by foreign turbines, and, for the implementation of the import substitution program, one can use the positive experience of PAO NPO Saturn in casting blades from IN738-LC alloy based on a reverse engineering technique. A preliminary complex of studies of the original manufacturer’s blades should be carried out, involving, first of all, the determination of geometric size using modern measurement methods as well as the studies on the chemical compositions of the used materials (base metal and protective coatings). Further, verifying the constructed calculation models based on the obtained data, one could choose available domestic materials that would meet the operating conditions of the blades according to their heat resistance and corrosion resistance.

Production Trial of a New Heat-Resistant Alloy with Low Density with Single-Crystal GTE Blade Casting

Under conditions of Klimov engineering enterprise, industrial results are obtained for the first time for developing casting technology for small single-crystal uncooled GTE turbine rotor blades of a new heatresistant alloy VZhM7 with reduced density and with a crystal orientation of . Structural models are developed for blocks of blades with seeds and heat-resistant alloy melting and pouring in a unit for directional solidification. Test batches of blade castings are obtained with a yield of finished single-crystal structure of not less than 90% under VIAM pilot plant conditions, and 80% under conditions of Klimov engineering enterprise. The structure and phase properties are given for single-crystal blade material after casting, hot isostatic pressing, and subsequent heat treatment. Data are provided for fatigue tests on blades with crystal orientation .

Investigation of operational characteristics of special-purpose alloy castings

Pilot smeltings of the intermetallic titanium alloy are performed during the work in the vacuum induction smelting installation with a “cold crucible” and the blades of a gas-turbine engine are fabricated by the casting method according to investment models in the centrifugal field. The structure of the initial charge billet for casting the intermetallic titanium alloy is investigated and its chemical composition is analyzed. The process parameters of casting and results of metallographic analysis of fabricated blades are presented. It is established that the cast blade structure has a lamellar structure and consists of phases γ and α2. The results of testing mechanical properties are presented. It is established that ultimate tensile strength σB = 765 MPa, yield point σy = 726.5 MPa, and relative elongation δ = 1.6%. The stress distribution on the blade pen is investigated and its distribution diagrams are constructed. Blade samples are tested for long-term strength (t = 650°C, τ = 500 h), fatigue strength, and impact toughness.

The Study of Nonmetallic Inclusions Formation for Kaplan Blades during the Solidification Process

The exploitation durability of Kaplan hydraulic turbines blades is first of all determined by their structure, by the steel elaboration technology, respectively by the content of non-metallic inclusions and later by the physical-chemical parameters of the exploitation environment.This paper presents a study regarding the situations in which the elaboration-casting technology of Kaplan blades using alloyed austenitic stainless steel, X5CrNiMo17-13-3 which has an important role in the quality of castings. Thus, the authors verify the formation of sulfides and of oxi-sufides during the steel elaboration process, treatment during a liquid state and their influence in the castings behavior to wearing. It is a well known fact that the presence of sulfides and oxi-sufides in the cast blades structure accelerates the corrosion process in contact with river waters.

Middle support layer formation and structure in relation to performance of three-tier thin film composite forward osmosis membrane

In recent years, nanofibers have been directly used as the support layer for developing high-flux forward osmosis (FO) membrane due to their high porosity and low tortuosity. However, the rougher surface and larger pore size weaken the adhesion to the polyamide (PA) active layer. Conventional FO membrane made of phase inversion support layer exhibits favorable mechanical stability, however the water flux is poor due to severe internal concentration polarization (ICP). In order to simultaneously reduce the ICP and enhance the mechanical stability of FO membrane, a thin film composite (TFC) FO membrane composed of three layers was prepared, namely bottom electrospun hydrophobic/hydrophilic interpenetrating network composite nanofibers (HH-IPN-CNF) support layer, a phase separation formed microporous polyvinylidene fluoride (PVDF) middle support layer, and the top PA active layer formed by interfacial polymerization. The factors including polymer concentration, coagulation bath composition and the gate height of the casting blade that affect the mid-layer structure formation were investigated, respectively. With the mid-layer of FO membrane cast under different conditions, water flux ranged from 10.39 to 30.62LMH, by using 0.5M NaCl draw solution and deionized water feed solution. The TFC FO membrane with high structure integrity may be promising candidate for engineered osmosis.

Investigation of operational characteristics of special-purpose alloy castings

The article reviews the experimental melting of an intermetallic titanium alloy in a vacuum induction melting unit equipped with a «cold crucible» and manufacturing of gas turbine engine blades by investment casting in a centrifugal field. It studies the structure of the initial charge blank intended for melting the intermetallic titanium alloy, and analyzes its chemical composition. The article presents the casting process parameters and results of the metallographic analysis of manufactured blades. It was found that the structure of the cast blade is lamellar and consists of phases γ and α2. The article provides the mechanical test results. It was found that the ultimate tensile strength was σв = 765 MPa, the yield point was σт = 726,5 MPa, the relative elongation was δ = 1,6 %. The article studies the stress distribution along the blade feather and constructs distribution diagrams. Blade samples were tested for long-term strength (t = 650 °C, τ = 500 h), fatigue strength, and impact strength.

Numerical simulation and experimental verification of gravity and centrifugal investment casting low pressure turbine blades for high Nb–TiAl alloy

Gravity and centrifugal investment casting processes of low-pressure turbine blades with high Nb–TiAl alloy were simulated by Procast software. Actual blade components were poured by vacuum induction suspended furnace with Ar protection. The experimental verification indicated that the simulation results were in good agreement with the experimental results. Comparative results had shown that the surface of centrifugal casting blade was more complete than that of gravity casting one. In gravity casting process, molten metal filled the thinnest trailing edge at last, resulting in the generation of misrun defects. Furthermore, the shrinkage porosity and crack defects of gravity casting were much more and dispersive. The internal and external quality of centrifugal casting was much better than that of gravity casting. Microstructures from edge to center of gravity casting blade had no significant change. The microstructure for centrifugal casting blade is finer than that for gravity casting blade, however, a large number of dentritic γ segregation appeared in the blade edge of centrifugal casting, which resulted from the fast cooling rate of centrifugal casting surface.

Improvement in Casting Technology of the Blades of Aviation Gas-Turbine Engines Made of TNM-1B1 Alloy in Conditions of Induction Crucible Smelting

Properties of the TNM-B1 alloy based on γ-titanium aluminide are investigated in order to find reliable results of simulation of casting processes used to fabricate the blades of gas-turbine aircraft engines. Thermal properties of the TNM-B1 alloy are experimentally determined using the methods of differential scanning calorimetry (DSC), laser flash (LFA), and dilatometry (DIL). Various variants of gate-feeding systems for the production of cast blades using a smelting-pouring installation for vacuum induction smelting («Consarc», Scottland) in conditions of JSC Ufa Engine Production Association. The test casting is obtained and its defects are analyzed. Good correspondence of results of modeling to actual centrifugal pouring of blades is shown.

Improvement in the casting technology of blades for aviation gas-turbine engines made of TNM-B1 titanium aluminide alloy produced by induction crucible melting

Properties of the TNM-B1 γ-titanium aluminide alloy are investigated in order to find reliable results of a simulation of casting processes used to produce the blades of gas-turbine aircraft engines. Thermal properties of the TNM-B1 alloy are experimentally determined using the methods of differential scanning calorimetry (DSC), laser flash analysis (LFA), and dilatometry (DIL). Various variants of gate-feeding systems for the production of cast blades using a vacuum induction melting furnace (Consarc, Scotland) in conditions of the Ufa Engine Production Association (OAO UMPO) are considered. The test casting is obtained and its defects are analyzed. A good correspondence of results of simulation to the actual centrifugal filling of blades is shown.

Mechanical Properties and Microstructure of IN738LC Nickel Superalloy Castings

IN738LC is a cast nickel-base superalloy developed for applications requiring high strength at elevated temperatures. Its balanced composition provides a good combination of tensile and creep-rupture properties as a result of gamma prime precipitate strengthening enhanced by solid solution and grain-boundary strengthening. Experimental castings are used in heat treated state. This alloy is used widely, for example, for manufacturing of gas turbine blades. Recently, customers demand different weight of castings hence different conditions during solidifying and cooling of the castings originate, resulting in different castings microstructure. When approving the castings, mechanical values are measured by tensile test on test bars made from the cast blade roots. This work investigates mechanical properties casting structure correlations, particularly grain, casting defects, carbides.