The dendrite coherency point (DCP) temperature refers to the state of a solidifying alloy at which a coherent dendrite network is established during the formation of grains. There are three main approaches for detection of DCP: (i) the thermal analysis method, (ii) mechanical (or rheological) technique and (iii) physical method based on the thermal diffusivity measurement technique.There are two basic variants of the thermal analysis method. In the late 1980's Bäckerud developed a method that utilizes two thermocouples. The DCP is determined by identifying the point of minimum temperature difference at the δT curve (TW–TC). Recently, has been revealed that utilization of the first derivative curve (dT/dt) plotted versus temperature also allows for analysis of the α-Al dendrite nucleation and growth characteristics and consequently determination of the DCT. This paper will illustrate that the dendrite coherency temperature could be identified by the 1st derivative curve (the one-thermocouple method) with the same accuracy as well as by using two thermocouples technique.

The strain amplitude dependent internal friction at room temperature and the transition temperatures of CuAlMn-shape memory alloys with Al contents from 8.9 wt.% to 12.7 wt.% and Mn contents from 4.7 wt.% to 9.3 wt.% were investigated. The investigated strain range was 10-6 - 10-3. Rods of various compositions were die cast and machined to single clamped damping bars. Their transition temperatures and amplitude dependent damping was determined in as cast and homogenized state. The damping in the investigated shape memory alloys was found to be generally much higher than in metals without martensitic transition. In as cast state some alloys exceeded the damping of a Sonoston type alloy measured in comparison for strains higher than 3 x 10-5. The influence of grain size on damping was investigated by additional sand casting and the use of Boron for grain refinement. It was found that only the material with the biggest grains had a noticeable higher damping over the whole measured strain range. Homogenization heat treatment can still extremely increase the damping of CuAlMn alloys. After homogenization this extremely high damping decreases slowly to medium values in the order of as cast alloys.

Alloys of CuAlMn are known as cheap, high strength shape memory alloys with an excellent damping capacity within their austenitic-martensitic phase transformation, compared to alloy systems like NiTi, CuZnAl or MnCu. But CuAlMn alloys have disadvantage due to generation of voids by a high shrinkage which further increases the existing proneness to stress cracks during rapid cooling. Alloying grain refining elements improves the stress crack resistance and enables a wide range of rapid quenching parameters which are needed to control the temperature of martensitic phase transformation. Additionally, the elements itself influence the in-or decreasing of the phase transformation temperature and the SMA effects. Furthermore, some of these elements can reduce the internal friction indirectly by decomposing areas of metastable martensite into its stabilized forms, where no transformation occurs. This thermic stability can be calculated by the concentration of valence electrons in a unit cell. The proneness to ageing is controlled by multistep heat treatments. Annealing and rapid quenching into the area of martensitic phase transformation maximize the generation of point defects. A high amount of point defects contradicts the negative effect of pinning. It also preserves the material from extreme brittleness. The influences of these effects are shown at single cantilever bending beams by elastic strain amplitude (ε = 12E-4) depending measurements of internal friction at natural frequency along the ageing at room temperature (293 K) up to 2500 h. The samples are annealed at 1123 K for 15 min (CuAl14Mn2) and 1100K for 30min (CuAl11Mn5) afterwards rapid quenched to 370 K with no further thermic stabilisation. The base alloy of CuAl14.1Mn2.0Ni1.9Fe0.4 had an internal friction measured as logarithmic Decrement (δ) of 0.155 and 0.11 after 2500 h of ageing at RT. The phase transformation is located between 284 K and 352 K, measured by DSC. The alloy of CuAl11.1Mn5.5Zn2.9Ni2.1 had a logarithmic decrement of 0.31 and diminish continuously to 0.12 after 2500 h of ageing at RT. The phase transformation is located between 287 K and 318 K.