Although it's often valuable to have ceramics and metals in the same device, joining them together is difficult-differences in heat expansion often cause cracking where the materials meet. One possible solution: Moving gradually from one material to another to spread the stress evenly, and yield a more stable joint. A new rapid prototyping technique developed at Sandia National Laboratories in Albuquerque, N.M., called robocasting, builds up hybrid parts by dispensing small amounts of a ceramic slurry. By mixing more nonceramic material into the slurry over time, Sandia's robot makes a graded part. Engineer Joe Cesarano says the robocast pieces, which can be created in less than 24 hours, have an additional advantage: They're denser than ceramic parts made by other rapid prototyping methods. The metal-ceramic parts would be particularly useful in engines that operate at very high temperatures, Cesarano says.

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