Refractory metal powders are dehydrided in a device which includes a preheat chamber for retaining the metal powder fully heated in a hot zone to allow diffusion of hydrogen out of the powder. The powder is cooled in a cooling chamber for a residence time sufficiently short to prevent re-absorbtion of the hydrogen by the powder. The powder is consolidated by impact on a substrate at the exit of the cooling chamber to build a deposit in solid dense form on the substrate.