High pressure turbine blade tips are critical for gas turbine performance and are sensitive to small geometric variations. For this reason, it is increasingly important for experiments and simulations to consider real geometry features. One commonly absent detail is the presence of welding beads on the cavity of the blade tip, which are an inherent by-product of the blade manufacturing process. This paper therefore investigates how such welds affect the Nusselt number, film cooling effectiveness and aerodynamic performance. Measurements are performed on a linear cascade of high pressure turbine blades at engine realistic Mach and Reynolds numbers. Two cooled blade tip geometries were tested: a baseline squealer geometry without welding beads, and a case with representative welding beads added to the tip cavity. Combinations of two tip gaps and several coolant mass flow rates were analysed. Pressure sensitive paint was used to measure the adiabatic film cooling effectiveness on the tip, which is supplemented by heat transfer coefficient measurements obtained via infrared thermography. Drawing from all of this data, it is shown that the weld beads have a generally detrimental impact on thermal performance, but with local variations. Aerodynamic loss measured downstream of the cascade is shown to be largely insensitive to the weld beads.

The microstructure and mechanical properties of materials produced by Wide Gap Brazing (WGB) and Laser Beam (LBW) cladding with different blends of Mar M247 and Amdry DF-3 brazing powders were studied. It was shown that LBW Mar M247 based materials comprised of 0.6 to 1 wt. % B were weldable. The weld properties were superior to WGB deposits with the same bulk chemical composition, due to the formation of a dendritic structure typical for welded joints, and the precipitation of cuboidal borides of Cr, Mo, and W in the ductile Ni-Cr based matrix. Both materials were found to have useful properties for 3D additive manufacturing (AM) and repair components manufactured from high gamma prime precipitation hardened superalloys.

Laser metal deposition (LMD) — also referred to as laser deposition welding — has been a well-established process for years. One example of its use is for tip repair for gas turbine blades from Siemens. The decision to also implement laser welding technology for the service of industrial steam turbines was based primarily on the fact that repairs — especially conventional welds and coatings including heat treatment and testing — are very time consuming and are very difficult to reconcile with the overhaul periods planned by customers. The robot supported automation of the LMD process and the fact of its lower heat input, reduced layer thicknesses and the resulting lowered deformation of the part due to reduced coating areas makes it possible to optimize lead times. The high level of process automation and reliability of a laser welding process represents another important benefit. Similarly, process parameters are constantly monitored and tracked, to ensure that the required quality standards are maintained and even increased. Furthermore, laser metal deposition completely replaced the conventional processes such as tungsten inert gas method (TIG), plasma transferred arc (PTA) and detonation spraying. In addition the technology unleashes now the possibility to repair and refurbish parts instead of new manufacturing, and therefore delivery times can be tremendously reduced. Based on the decision to six-axis robots it becomes possible enhancing the LMD process for complex 3D surfaces. After modeling a digital twin in Siemens NX CAM it is possible to generate, optimize and simulate the whole motion-sequences offline before starting the LMD process in the robot cell. So already designed parts in 3D-CAD can be used to develop the final robot program. In addition already existing technologies like 3D surface scanning will be implemented in the chain to support the LMD process. Digitalization turns from a buzzword to an established technology for industrial steam turbine manufacturing and repair.

This paper begins with a statement of the acceptance and use of inertia welding in the gas turbine field. A short explanation of the inertia welding process follows. Categories of welds discussed are solid inertia butt welds; tubular inertia butt welds; and angular-annular inertia butt welds. An example of the first category is a bimetallic engine valve. The second category is typified by steel shafts joined to superalloy rotors for turbines. The joining of wrought superalloy disks to cast superalloy blade rings to produce a composite wheel comes into the third category. The effect of welding parameters on strength and microstructure, as well as design and process changes required for inertia welding are related. In conclusion, basic considerations for utilization of inertia welding are expressed.

The methodology and the procedure of diagnosis of a cracked stationary blade of a compressor due to high cycle fatigue is presented. The natural frequencies of the blades and a st a tor row were measured and an analysis of the casing vibrations during start-up and under load conditions of the compressor was conducted in a search for the cause of the failure. Using finite element code the natural frequencies and the vibratory stresses of the stator row blades (vanes) were computed. The computed maximum vibratory stresses in the vane were concentrated in the location of the crack which originated from the welded joint. It was concluded that the welded joint requires modification.

Alpha-two titanium aluminides represent strong candidates for replacing many conventional titanium and nickel-base superalloys for intermediate temperature applications. One potential application of these alloys is turbine engine rings. Nonrotating rings of this type are typically manufactured by flash butt welding. The performance of welds in this alloy are known to be strongly affected by the weld microstructure. Welding processes that result in very slow cooling rates yield relatively coarse Widmanstatten-type microstructure(s) which generally yields acceptable weld performance. Processes that result in intermediate cooling rates, however, result in acicular alpha-two martensite microstructures. These microstructures have very little ductility and lead to reduced weld performance. Finally, for processes where the cooling rate is very rapid, the weld microstructure is a retained ordered beta phase, which apparently results in improved weld properties.

A metallurgical investigation was conducted on transitions from two land-based 105 MW gas turbines. One transition suffered catastrophic failure, and two transitions had cracking at the top panel. Two alloys, IN-617 and a modified IN-617, were used in these transitions. The investigation consisted of thickness measurements, optical and scanning electron microscope fractographic studies, metallography, EDS and Auger analysis of precipitates, chemical analysis, and hardness measurements. In both units, heavy oxidation of the top panel on the hot gas side (inside) occurred. Oxide intrusion along the grain boundaries and exfoliation of the oxide layer occurred. This caused thinning of the panel with a resultant loss of about 50% of the panel thickness. Bulk creep cavitation along the grain boundaries and multiple discontinuous creep cracks were present. Crack origins were located at the outer surface of the top panels. Creep cracks and cavities, carbide precipitates, agglomeration of grain boundary carbides, and aluminum nitride were present in the microstructure. The primary cause of cracking was the increase in net section stress, which exceeded the creep strength of the panel. The effect of microstructural changes on the formation of cracks was secondary in nature. Cracks were not associated with welds.

A research study was undertaken to evaluate whether electron beam welding (EBW) or gas tungsten arc welding (GTAW) could be utilised for repairs to the leading edges of the Turmo IV C compressor blades. These blades are manufactured from Ti-6Al-4V. The study entailed performing a series of welding trials. For the GTAW process a matching filler metal to the parent metal was used whereas for the EBW process, the welds were made autogenously. After metallographic examination of the weld microstructure, mechanical property assessments were undertaken, namely tensile and fatigue tests, the latter being a stringent test to evaluate the performance of the welded joint. The results demonstrated that the EB welds had equivalent properties to the parent metal whereas the GTA welds had poorer fatigue properties due to undesirable microstructure that resulted in the weld zone. The results achieved herein showed that the EBW process would be an appropriate technique for the restoration of these compressor blades.

This research study was undertaken to evaluate whether gas tungsten arc welding (GTAW) could be utilised to extend the limits of an existing repair scheme. The compressor impeller of the GTC 85-71 suffers from such severe sand erosion to the leading edges, that the damage exceeds the manufacturers specification. The impeller is manufactured from Ti-6Al-4V. The study entailed performing a series of welding trials and post-weld heat treatments. After metallographic examination of the weld microstructure, mechanical property assessments (i.e. tensile and fatigue tests) were undertaken. The results demonstrated that the welds after the 550 °C/8 hr post-weld heat treatment had equivalent properties to those of the parent metal. The stress distribution determined by finite element analysis showed the weld to be in an area of low stress. The results achieved herein and the stress analysis showed that the GTAW process is feasible for extending the repair limits for restoration of the leading edges of the compressor impeller.

In many advanced combustor concepts, such as the RQL (rich-quench-lean) combustor, the requirement of low NOx emission makes film cooling of the hot gas path surfaces undesirable. Double-walled structures with relatively low aspect ratio (height/width) rectangular passages and with well-controlled thin hot gas side metal walls are an alternative to film cooling. The additional application of other cooling techniques, such as impingement and surface enhancements, make efficient use of the limited cooling air available. However, the use of cooling channels to increase heat transfer coefficients on the coolant side may ultimately require well-bonded structures. Alternate methods of bonding have been considered for Ni-base alloy HA230-to-HA230 joints in thin-walled structures, with emphasis on bonds produced by hot isostatic pressing and by laser welding. For hot isostatic pressed (HIPed) structures, mechanical strength and ductility have been measured as a function of temperature for structures prepared after a number of different surface cleaning treatments prior to joining. The surface cleanliness has been characterized by scanning electron microscopy, and the after-HIP bond line microstructure has been evaluated as formed and after mechanical testing. Characterization of laser welds produced at Laserdyne for Acraline Products has consisted of scanning electron microscopy of the weld surfaces and metallography of weld/substrate cross-sections, looking at solidification/heat affected features and defects.

Several fusion repair processes such as laser cladding, laser welding and gas tungsten arc welding have been taken into consideration for repairing IN738 precipitation hardened Ni-based superalloy material. Effect of heat input on weld cracking susceptibility has been studied to obtain optimum condition for crack free welds. Variations in cracking susceptibility as a function of welding heat input is discussed with reference to metallurgical characteristics of the welds.

The properties of laser, microplasma and GTAW welds on representative gas turbine blade materials are disclosed. Proprietary filler materials and technology were used to clad multipass welds onto IN738, RenéN5 and CMSX4 alloys which were then subject to vacuum heat treatment before testing. It was found that welds with a bulk content of boron up to 0.6 wt. % demonstrated a capability to heal cracks adjacent to the fusion line (HAZ cracks) and they exhibited superior tensile and stress-rupture properties at a temperature of 982°C. Welds that comprised 1.5 to 2% silicon had superior oxidation resistance at a temperature of 995°C. Combined alloying of welds with moderate amount of boron and silicon produced a unique combination of both high mechanical and oxidation properties. Healing of HAZ cracks took place during post weld heat treatment at a temperature exceeding the solidus temperature of the weld metal eutectics but below of a solidus temperature of the base material. It was found that boron and silicon additives reduced welding pool solidification temperature and increased the solidus–liquidus range. At this temperature a partial re-melt of eutectics occurred allowing healing of HAZ and weld solidification cracks while weld geometry was supported by a continuous framework of high temperature dendrites. This allows the tip repair of turbine blades manufactured of precipitation strengthened superalloys that are normally prone to weld cracking.

Fossil fired steam power plants of the latest generation require the elevation of steam parameters pressure and temperature to increase efficiency as well as to reduce greenhouse gas emissions. In order to achieve these goals for high temperatures, nickel base alloys could play an important role for steam turbine applications in the future. Due to technological and economical restrictions, their application in turbine rotors shall be restricted to the most heavily stressed regions. Dissimilar welds offer a known solution to combine nickel base alloys with ferritic/martensitic steels in this case. Thermal mismatch and differences in high temperature performance of the applied base materials make it very difficult to evaluate the lifetime of such dissimilar welds. Depending on temperature and type of loading, different failure mechanisms can be observed. Further, the type of weld material plays a major role for the service behavior of the weld. Therefore, this paper describes standard creep and fatigue tests which were conducted to identify failure mechanisms and failure locations at the weld zone. To simulate the outcome of the creep tests, a modified Graham-Walles approach is used that also accounts for the different creep behavior of the heat affected zones compared to the base material. For the simulation of the fatigue tests, the model type CNOW (Chaboche-Nouailhas-Ohno-Wang) is used. The results contribute to better knowledge in designing dissimilar welds between nickel base alloys and martensitic steels under high temperature loading.

In order to ensure safety and reliability of steam turbine welded rotors, the present investigation focuses on evaluation of crack initiation, growth, and resistance parameters of base metal (BM), weld metal (WM) and heat affected zone (HAZ) of a steam turbine rotor welded joint constituent. The experimental part consists of three-point bending conducted on single edge notch bend specimens to induce stable crack propagation. The crack size was calculated by incorporating the crack opening displacement measured by a clip-gage, in a compliance method. The fatigue crack threshold was obtained from a crack growth rate curve according to ASTM E647 and the fracture toughness was determined from a J -based resistance curve according to ASTM E1820. From the experimental results the fatigue crack threshold is found to be a function of loading ratio rather than a single material parameter. From the fracture toughness results, the WM and the BM are found to have similar K Ic values whereas HAZ is found to have slightly better K Ic values although HAZ had little crack extension during the experiments.

Nowadays high-strength steels have great applications in different industries due to their good combination of formability, weldability, and high strength-to-weight ratio. To guarantee a high quality without the presence of defects such as partial penetration (PP) in the laser welding of high-strength steels, it is very important to on-line monitor the whole welding process. While optical sensors are widely applied to monitor the laser welding process, we are proposing to use a microphone to acquire the airborne acoustic signals produced during laser welding of high-strength steel DP980. In order to extract valuable information from a very noisy signal acquired in a harsh environment such as industrial welding, spectral subtraction (SS), a noise reduction method is used to process the acquired airborne sound signals. Furthermore, by applying the power spectrum density (PSD) estimation method, the frequency characteristics of the acoustic signals are analyzed as well. The results indicate that the welds in full penetration (FP) and PP produce different signatures of acoustic signals that are characterized with different sound pressure levels and frequency distributions ranging from 500 Hz to 1500 Hz. Based on these differences, two algorithms are developed to distinguish the FP from PP during the laser welding process. A real-time monitoring system is implemented by a LabVIEW-based graphic program developed in this research. A feedback control system that could guarantee the FP will be developed in the near future.

The primary structure of the ARES I-X Upper Stage Simulator (USS) launch vehicle is constructed of welded mild steel plates. There is some concern over the possibility of structural failure due to welding flaws. It was considered critical to quantify the impact of uncertainties in residual stress, material porosity, applied loads, and material and crack growth properties on the reliability of the welds during its pre-flight and flight. A criterion — an existing maximum size crack at the weld toe must be smaller than the maximum allowable flaw size — was established to estimate the reliability of the welds. A spectrum of maximum allowable flaw sizes was developed for different possible combinations of all of the above listed variables by performing probabilistic crack growth analyses using the ANSYS finite element analysis code in conjunction with the NASGRO crack growth code.