Reliable mechanical tests on CFCs joined to heat sinks are still an issue. As ASTM tests to measure the shear strength of CFCs joined to metals are not available, several laboratories have independently developed tests for CFC to metal joints, making interlab comparison of results almost impossible. Joints obtained by AMC® have been extensively tested,146 in particular for shear strength, with data ranging from 20 to 60 MPa for prepared samples. At 600 °C, the shear strength dramatically decreases to ^20 MPa. The shear strength and tensile strength of the improved AMC® (TiSi-AMC) joint are in the range of 54—73 MPa and of 39—64MPa, respectively.130,146

Monoblocks obtained by AMC® have been measured after HHF tests147: apparent shear strength has been measured in the range of 30—60 MPa. Some cracks have been found at ±45°, ±90°, and ±135°, considering 0° as the flux direction, leading to the de­tachment of CFC from the Cu layer before testing.148 The Cr-modified CFC—Cu joined samples148-152 have been measured by single-lap test (adapted from ASTM C 1292, C 1425) and off-set single lap test (adapted from ASTM D 905) at room temperature. Independent of the CFC surface machining and different casting process, results obtained133,138 for Cr-modified CFC on more than 50 samples yielded average values of apparent shear strength ranging from 26 to 32 MPa. The average shear strength is in any case higher than the interlaminar shear strength of the CFC (15 MPa).

The shear strength of the CFC—Cu joints (flat-tile geometry) obtained by using a commercial Gemco® brazing alloy to braze CFC to pure copper was 34 ± 4 MPa, measured by single lap tests at room temperature. This is comparable to the values obtained by other joining processes and higher than the intrinsic CFC shear strength.140

Mechanical tests on the monoblock braze require specific designs: some of them are adapted by ASTM D 4562-01 ‘‘Standard Test Method for Shear Strength of Adhesives Using Pin-and-Collar Speci­men’’, as in the compression test used by Plansee AG, but the joint is not stressed in uniform pure shear state.

Reliable nondestructive tests (NDTs) are also extremely important for nuclear fusion components, especially for high heat flux PFCs. NDTs on CFC—Cu joints are complex because of the different response of CFC and copper to the physical excitations used to test the component. The aim of NDT is to identify and localize defects in the joined components before submitting them to high heat flux tests or actual appli­cation. It is also important to identify the maximum acceptable defect size, as a function of its position, defined as the largest defect that is stable under spe­cific loads in the fusion device.139,149 Several techni­ques are used for NDT150: X-ray microradiography, X-ray microtomography, ultrasonic inspection,151,153 lock-in thermography,1 2 and transient infrared ther­mography (SATIR). SATIR (Figure 42) is the French acronym for infra red acquisition and data proces­sing device: it is a dedicated facility developed in Cadarache-France at CEA. SATIR consists of record­ing the surface temperature evolution of the compo­nent with an infrared device during the circulation of hot (^95 °C) and cold (~5 °C) water through the cooling channel of the component. The transient ther­mal response is compared to a ‘defect-free’ component; defects such as debonding of CFC tiles from heat sinks are detected by a slower temperature surface response (Figure 42).

Ultrasonic inspection has been applied to the flat tile and the monoblock design. Defects on joints between materials having very different acoustic impedance (e. g., copper and CFC) result in the gen­eration of a high reflected echo, making defect detectability more difficult.141 Lock-in thermogra­phy consists of applying a series of heat flashes on the CFC. The main advantage of this technique is that there is no need for an active cooling of the component and it can also be used as an inspection method during the manufacturing process.142,152

Several nondestructive tests have been performed on the Cr-modified CFC—Cu joined samples150 not only to test performance, but also to verify and compare the reliability of these tests on a CFC—Cu interface. However, the present conclusion is that nondestructive tests of joints should be validated by destructive tests such as morphological evidence of the detected defect and mechanical testing.