YILDIZ TEKNİK ÜNİVERSİTESİ MAKİNE MÜHENDİSLİĞİ BÖLÜMÜ HARDNESS AND FRACTURE TOUGHNESS OF ATMOSPHERIC PLASMA SPRAYED YTTRIA-STABLIZED ZIRCONIA THERMAL BARRIER COATINGS ALI AVCI AYSEGUL AKDOGAN EKER Yildiz Technical Universty, Istanbul, 34349, Turkey International Journal of Arts&Sciences FREIBURG CONFERENCE Nov 28-Dec 02, 2016

History of TBCs Firstly, thermal barrier coatings were developed1950s by NASA. These studies aimed to protect from hot effect. After 1970s TBCs were used in gas turbine combustion chamber. In the advancing decedas, Al2O3 , mullites were used as a TBCs however their mismatch between thermal coefficient of expension of metals.

abstract Thermal barrier coatings (TBCs) are commonly used in gas turbines hot section components sach as burners, blades, vanes TBCs protect the substrates and turbine components against to thermal effect and increase turbine efficiency. It is important to increase toughness and hardness of the TBCs due to hot gasses effect and thermal shock.

Why TBCS are Important Generally, Ceramic coatings on the materials surfaces are economic to protect the materials from corrosion, wear, hot effect etc. Thanks to surface modification provides needed features morever metalic substrates preserve their toughness, machinability and durabilty etc TBC consist of three layers; One of them bond coat, * to protect metalic substrate from oxidation wear corrosion * To provide thermal adaptation between substrate and top coat(ceramic) Other one is ceramic top coat; * Insulation layer from hot gas or thermal effect * Wear resistance Last one is metalic substrate ; * It can work high temperature almost %90 of melting temperature * To provide toughness, durabilty and matrix * Generally super alloys are used as substrate because of ıts hıgh feature such as high melting temp.

Demostration of a TBC system which is applied to turbine vane to serve as a thermal insulator

Material and methot Using the stainless steel as substrate NiCrAlY commercial (Amdry 962) powder was deposited on to AISI304 stainless steel substrates as a bond coat using high velocity oxygen and fuel methot (HVOF). Yttria-stabilized zirconia (YSZ) and Al2O3 coatings composite powders were deposited as a top coat using by atmospheric plasma spray APS on the bond coat

Produced steps of TBCs APS Coating System Scaning electron microscope investigation Cutting and polishing processes Micro Vickers methot

In the present study, The coatings toughness and hardness were investigated to be dependent on the Al2O3 rate that affects coating hardness, toughness and microstructural features. The fracture toughness and hardness was measured using micro Vickers indentation technique and the micro structure was observed to show micro cracks using by (SEM) scanning electron microscopy.

Coatings power microstructural Power material Chemical Comp. Grain Shape Grain Size Density (g/cm3) YSZ ZrO2 8Y2O3 Spheral -75 +45 μm 5,9 Al2O3 2 wt.% SiO2-98 wt.% Al2O3 -45 +15 μm 3,9 Amdry 997 Ni 23Co 20Cr 8.5Al4 Ta 0.6Y - 38 +5 μm ---  

Processes parameters of coating Material Pressure(bar) Flow Rate Processes AMDRY 997 Oxygen Propan Air Spray Distance (mm) Power Feed Rate (g/min) 10.3 6.2 7.2 24 40 50 250

Sem INVESTIGATION OF COATINGS

Vickers Hardness Value Test was applied randomly 12 differetnt point on the samples by by HVS 1000 micro vickers hardness devices. Load was determined 300 g and loading time was 15 s. Before the hardness test all sampless polishing test.

Hardness Vickers

conclusions Adding to AL2O3 is increasing hardness at YSZ While porosity is getting high the hardness is falling Vickers hardness values depending on the alumina ratio.. The values is changing between 1032 HV to 1491 HV While hardness is increasing the wear resistance is increasing(as well mechanic strength) Alumina ratio increase the density , decrease the porosity Alumina protect to coatings from oxygen attack, corrosiaon and hot gas affect

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