CORDIS Database: RESULTS
Development of bonding for diffusion barriers for the high 
temperature blades of gas turbines

Record Control Number : 26629
Quality Validation Date : 2001-07-24
Update Date : 2001-07-24
Abstract : The goal of the present basic research project was to develop 
		suitable and reliable bondings for the diffusion barrier layers 
		developed in a previous project of the European concerted action 
		COST 501/II, WP 7A for delaying the detrimental diffusion of nickel 
		and aluminium between the nickel base super-alloy blades and their 
		MCrAlY type overlay at temperatures at and below 1100 degrees 
		Celsius. This detrimental diffusion between the mentioned materials 
		starts actually at about 950 degrees Celsius depending on the 
		composition of the super-alloy used in the blades. In the present 
		project, the diffusion barriers inherited from the earlier project 
		were an amorphous layer of Al-O-N and a trible layer of TiN+AlN+TiN,
		the former developed by RWTH.LFWW, and the latter by TUT.DMS. The 
		substrate super-alloys were IN738 LC in the polycrystalline form 
		and SRR 99 in the single crystalline form, the former one used in 
		land-base as well as in aero gas turbines and the latter one mostly 
		in aero gas turbines. For both of the super-alloys, the dissolving 
		temperature of their Ni3Al precipitates is about 1050-1150 degrees 
		Celsius. This means that the super-alloys lose their strength at 
		and above these temperatures. This is why the temperature of 1100 
		degrees Celsius was taken as the maximum checking temperature for 
		the developed bonding. As IN738 at this temperature is already in 
		its softened state, i.e., it strains more easily than in its 
		hardened state, this extra strain causes extra requirements for the 
		bonding and in that way insures the reliability of the bonding.
		The overlay materials were LCO22 and Amdry 995, which have almost 
		the same composition. 
		
		A continuously changing gradient bonding appeared not to be 
		suitable for either of the cases. Therefore, a solution was 
		searched from special alloying of the barrier layer and from using 
		a separate bonding layer or layers. On the basis of annealing tests,
		a (semi) crystalline barrier layer of Al2O3 appeared to be as good 
		as or better barrier layer than the amorphous Al-O-N layer. Thus, 
		this new layer replaced the original one. For this new layer, an 
		alloying with 1% Y2O3 or a separate bond layer of Y2O3 appeared to 
		be promising solutions for the bonding. These solutions were tested 
		by mechanical bending at different temperatures, by scratch tests 
		at room temperature, by annealing at 1100 degrees Celsius and by 
		thermal cycling between room temperature and 1100 degrees Celsius. 
		In perpendicular blasting at room temperature by glass bolls under 
		a pressure of 5 bar, the bonding failed and the diffusion barrier 
		and its sputtered overlay spalled off entirely. Thus, the 
		roughening of the surface of the sputtered overlay required for the 
		further thickening of the overlay by means of plasma spraying is 
		not an applicable method for the developed bonding.
		
		In the triple type barrier layer, the outermost layers were of TiN. 
		Thus, the search of the bonding was directed to the bonding of TiN 
		to the substrate and to the overlay materials. After thermodynamic 
		evaluations and extensive laboratory scale tests on small specimens,
		seven promising candidates were found for the bond layer. The 
		bonding quality of these candidates were tested first by tensile 
		tests at room temperature, then by long term annealing, and by long 
		term thermal cycling between room temperature and 1100 degrees 
		Celsius. Additional reliability was searched through cyclic 
		mechanical stressing under different constant amplitudes at 1100 
		degrees Celsius, and by cycling of temperature between 850 degrees 
		Celsius and 1100 degrees Celsius under a constant loading of 100 
		MPa. In the simulating burner rig tests, maximum temperatures was 
		1100 degrees Celsius and the minimum 850 degrees Celsius. The 
		simulating high temperature corrosion tests ( the salt spray tests) 
		were done at 900 degrees Celsius, at the temperature of maximum 
		corrosion rate, and the spraying of salt liquid took place daily at 
		room temperature. From the candidate bondings, the layers of 6bv2 
		and 6bv3 (as such or as nitrided towards the surface against TiN)  
		passed these tests and the above mentioned blasting test 
		successfully. Therefore, these bond layers as suggested for the 
		bonding of the diffusion barriers in the subsequent industrial 
		development project.
		
		In the long term annealing as well as in the long term thermal 
		cycling tests, the single layer of TiN appeared to be a sufficient 
		diffusion barrier comparable to that of the earlier developed 
		triple layer. Thus, no need exists for using the more complicated 
		diffusion barrier at or below the temperature of 1100 degrees 
		Celsius.
		
		An additional goal in the original project plan was the development 
		of a non-destructive testing method, which could be used, with 
		certain reliability, as a quantitative test of the adhesion 
		strength (bonding strength)  between the super-alloy substrates and 
		their different coatings. As the ultrasonic nor the thermal 
		vibration used were capable of creating detectable yielding at the 
		interfaces, the developed ultrasonic method remained on qualitative 
		level. An inverse relationship was, however, detected between the 
		non-linear parameters of the ultrasonic measurements and the 
		tensile strengths of interfaces measured at room temperature.
Subject Descriptors : Metals, alloys, Materials handling
Subject Index Codes : Materials Technology, Industrial Manufacture
Subject Class : Materials, industrial manufacturing technologies
Market Applications : Aerospace
Collaboration Sought : Further research or development support, Information exchange
Collaboration Detail : For the success of the subsequent industrial project it is 
		important that the consortium includes:
		-An industrial coating company capable of using sputtering as well 
		as other PVD coating systems, for example, ion plating and advanced 
		thermal spraying.
		-Industrial producer or user of aircraft as well as power plant gas 
		turbines.
		-Participant(s)  capable of providing material and blades of CMSX 4,
		SRR 99 or other advanced super-alloys.
		
		As CESI/ENEL and AEROSPACE fulfil the second requirement, 
		collaboration is sought in the first and third requirement, i.e., 
		as concerning industrial coating company and materials provider.
Programmes : BRITE/EURAM 3
Projects : BRPR970389
Project Title : Development of Bonding for Diffusion Barriers for the High 
		Temperature Blades of Gas Turbines

Contact Details
  Contact Name : KETTUNEN, Pentti Olavi
  Department : Department of Materials Engineering
Institute of Materials Science
  Contact Organisation : Tampere University of Technology
  Address : korkeakoulunkatu 2
PO Box 589
  City : Tampere
  Region : MANNER-SUOMI
ETELÄ-SUOMI
Pirkanmaa
  Postcode : 33101
  Country : FINLAND
  Telephone Number : +358-33-162280
  Fax Number : +358-33-162330
  Electronic Mailbox : pentti.kettunen@c.c.tut.fi

 




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