The Application of the Small Punch Tensile Test to Evaluate the Ductile to Brittle Transition of a Thermally Sprayed CoNiCrAlY Coating

2017 ◽  
Vol 734 ◽  
pp. 144-155 ◽  
Author(s):  
G.A. Jackson ◽  
Wei Sun ◽  
D. Graham McCartney
Keyword(s):  
Tensile Test ◽  
Room Temperature ◽  
Free Standing ◽  
Small Punch ◽  
Bond Coats ◽  
Brittle Transition ◽  
Barrier Coating ◽  
Ductile To Brittle Transition ◽  
Conicraly Coating ◽  
Thermally Sprayed

Thermally sprayed MCrAlY bond coats are important elements of thermal barrier coating (TBC) systems which are applied to the surface of gas turbine components to protect them in high temperature environments. Knowledge of their mechanical properties is essential in preventing TBC failure which can have catastrophic consequences. However, limited data on modulus, strength and ductility are available for such coatings. In this work, the ductile to brittle transition behaviour of a CoNiCrAlY coating has been investigated via the small punch tensile test (SPTT). Displacement controlled tests were carried out on free standing coatings at room temperature (RT) and between 400-750 °C at a rate of 1 μms-1. At low temperatures there was evidence of elastic-brittle behaviour and at high temperatures there was clear evidence of yielding and plastic deformation. The ductile to brittle transition temperature was found to be between 500-750 °C. The yield stress ranged from 1000-1500 MPa below 600 °C to less than 500 MPa above 650 °C. The elastic modulus was found to be approximately 200-230 GPa at 500 °C and 55 GPa above 700 °C. At room temperature the fracture surface showed flat, smooth features indicating brittle failure whereas at 700 °C there was evidence of ductile tearing.

Evaluation of the ductile-to-brittle transition temperature in a thermally sprayed CoNiCrAlY coating by small punch multi-step loading tests

2016 ◽  
Vol 231 (1-2) ◽  
pp. 6-13
Author(s):  
H Chen ◽  
J Yang ◽  
XL Xiao
Keyword(s):  
Transition Temperature ◽  
Elevated Temperatures ◽  
Free Standing ◽  
Small Punch ◽  
Brittle Transition ◽  
Loading Tests ◽  
Step Loading ◽  
Brittle Transition Temperature ◽  
Ductile To Brittle Transition ◽  
Conicraly Coating

High velocity oxy-fuel thermal spraying was used to prepare free-standing CoNiCrAlY (Co–31.7%Ni–20.8%Cr–8.1%Al–0.5%Y, all in wt%) coatings of an approximate thickness of 0.5 mm. Small punch tests under multi-step loading conditions were performed between room temperature and 600 ℃ on these samples to evaluate the ductile-to-brittle transition temperature. The microstructure of the coatings was characterised using a scanning electron microscope with energy-dispersive X-ray analysis. A two-phase structure consisting of fcc γ-Ni and bcc β-NiAl was found to exist. The displacements obtained from small punch multi-step loading tests at each load increment were relatively small and similar at temperatures below 500 ℃ but a significant increase in displacement was noted at 600 ℃. Fractographic investigation showed that the main fracture mode was dominated by extensive γ matrix tearing at elevated temperatures. A distinct stress and strain behaviour was found at 600 ℃, indicating that the ductile-to-brittle transition temperature of this CoNiCrAlY coating occurred between 500 ℃ and 600 ℃.

Effect of Strain Rate on Ductile-to-Brittle Transition Temperature of a Free-Standing Pt-Aluminide Bond Coat

2011 ◽  
Vol 42 (6) ◽  
pp. 1431-1434
Author(s):  
Md. Zafir Alam ◽  
D. Chatterjee ◽  
K. Muraleedharan ◽  
T. K. Nandy ◽  
S. V. Kamat ◽  
...  
Keyword(s):  
Transition Temperature ◽  
Strain Rate ◽  
Bond Coat ◽  
Free Standing ◽  
Brittle Transition ◽  
Brittle Transition Temperature ◽  
Ductile To Brittle Transition

Use of the Master Curve to Investigate the Effect of Post-Weld Heat Treatment on ASTM A106B

2008 ◽  
Vol 41-42 ◽  
pp. 483-489
Author(s):  
N. Driessen ◽  
Richard E. Clegg
Keyword(s):  
Heat Treatment ◽  
Transition Temperature ◽  
Room Temperature ◽  
Post Weld Heat Treatment ◽  
Design Standards ◽  
Brittle Transition ◽  
Mechanics Analysis ◽  
Plant Operations ◽  
Ductile To Brittle Transition ◽  
Weld Heat

ASTM A106/B is commonly used for pressure piping in alumina refineries. Due to the problem of caustic cracking in alumina refineries, piping must be stress relieved after welding, usually through a post-weld heat treatment (PWHT) process at a temperature of 635°C. However, multiple PWHT procedures tend to degrade the mechanical properties of steel and design standards have set limits on the length of time PWHT can be carried out before steel should be replaced. In this study, the effect of PWHT time on the properties of A106/B parent metal was examined, with particular emphasis on the effect on toughness. PWHT was carried out for 1, 8 and 40 hours and the results were compared with those for as-received material. Impact transition temperature and room-temperature tensile results were determined using standard tests. The reference temperature, To, was determined using ASTM E1921 with arc-shaped tension specimens. The results showed that the ductile-to-brittle transition temperature increased significantly as PWHT time increased and the implications of this to a fracture mechanics analysis of plant operations are discussed.

Development and Standardization of Small Punch Testing Techniques in China

2016 ◽  
Author(s):  
Kaishu Guan ◽  
Limeng Xu ◽  
Cheng Wen ◽  
Jiru Zhong
Keyword(s):  
Transition Temperature ◽  
Specimen Thickness ◽  
Test Machine ◽  
Bending Stress ◽  
Small Punch ◽  
Elastic Bending ◽  
Brittle Transition ◽  
Element Simulation ◽  
Brittle Transition Temperature ◽  
Ductile To Brittle Transition

In the recent years, small punch testing (SPT) techniques has made great progress in China. The SPT was studied to estimate the tensile properties, the fracture toughness and ductile-to brittle transition temperature, and the creep behavior. In 2012, a standard of small punch testing was issued in China and the application of SPT in power generation and petrochemical industry has become a prime candidate. The present paper concentrates on progress of technique and standardization and industrial acceptance in assessing the structure integrity in China. China has carried out close cooperation with Material & Metallurgical research Ltd in Czech to compare Standards between China and EU code. The size of specimen and jig was researched and compared each other. The influence of jig and test machine was researched and improved the specific requirement of jig and test machine. The evolution of stress state of deformation process of specimen in SPT was clarified. The results showed that at initial stage the elastic bending stress is predominant and then the stress state dominated by membrane stress with the decreasing of elastic bending stress and the increasing of punch displacement. The reason for introducing the specimen thickness h2 to the equation for correlating yield load of SPT with yield strength, and the reason for introducing specimen thickness h to equation for correlating the maximum load of SPT with tensile strength were provided respectively. The correlation equation of ductile to brittle transition temperature and SPT energy transition temperature TSP was established and it was successfully used to evaluate embrittlement of hydrogenation reactor. Small punch creep testing by reverse finite element simulation was carried out and used to evaluate the creep life in power generation industry. Fracture toughness and Master curve using SPT by reverse finite element simulation combined with local approach was studied.

The High Temperature Creep Properties of a Thermally Sprayed CoNiCrAlY Coating via Small Punch Creep Testing

2017 ◽  
Vol 734 ◽  
pp. 37-48 ◽  
Author(s):  
G.A. Jackson ◽  
Hao Chen ◽  
Wei Sun ◽  
D. Graham McCartney
Keyword(s):  
Bond Coat ◽  
Gas Turbines ◽  
Creep Behaviour ◽  
Thermal Spraying ◽  
Thermally Grown Oxide ◽  
Creep Properties ◽  
Small Punch ◽  
Hvof Thermal Spraying ◽  
Conicraly Coating ◽  
Thermally Sprayed

Thermal barrier coatings (TBC’s) protect superalloy components from excessively high temperatures in gas turbines. TBC’s comprise of a ceramic top coat, a metallic bond coat and a thermally grown oxide (TGO). The creep behaviour of the MCrAlY bond coat, which is sensitive to the composition and the method of deposition, has a significant effect on the life of the TBC. High velocity oxy-fuel (HVOF) thermal spraying is a popular deposition method for MCrAlY bond coats however the creep properties of HVOF MCrAlY coatings are not well documented. The creep behaviour of a HVOF thermally sprayed CoNiCrAlY coating has been determined by small punch creep (SPC) testing. Tests were conducted between an equivalent uniaxial stress range of 37-80 MPa at 750 °C on two different SPC rigs and between 30-49 MPa at 850 °C on a single SPC rig. The measured steady-state creep deformation rates at 750 °C were consistent across the two rigs. A comparison with previous work demonstrated that the creep behaviour of HVOF CoNiCrAlY coatings is not sensitive to the manufacturing variability associated with HVOF thermal spraying. The CoNiCrAlY coating exhibited typical SPC deformation at 750 °C. At 850 °C the CoNiCrAlY coating showed significantly different creep behaviour which could be attributed to the onset of superplasticity.

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