# Hydrothermal Hot Isostatic Pressing (HHIP)—Experimental Proof of Concept

## TL;DR

A new hydrothermal hot isostatic pressing method was developed to reduce pores in 3D-printed aluminum parts at lower temperatures.

## Contribution

The novel HHIP approach eliminates inert gas and achieves significant pore reduction at lower temperatures.

## Key findings

- The new HHIP method reduced micro-pores by 85.7% and surface area by 90.8%.
- The treatment caused minimal material loss (<0.5% w/w) due to corrosion.
- The method preserved the microstructure and could improve mechanical properties without affecting fatigue resistance.

## Abstract

A new hydrothermal hot isostatic pressing (HHIP) approach, involving hydrothermal water conditions and no usage of inert gas, was hypothesized and tested on 3D-printed Al-10%Si-0.3%Mg (%Wt) parts. The aluminum-based metal was practically inert at the applied HHIPing conditions of 300–350 MPa and 250–350 °C, which enabled the employment of a long (6–24 h) HHIP treatment with hardly any loss of material (the overall loss due to corrosion was mostly <0.5% w/w). Applying the new approach on the above-mentioned samples resulted in an 85.7% reduction in the AM micro-pores, along with a 90.8% reduction in the pores’ surface area at a temperature of 350 °C, which is much lower than the 500–520 °C applied in common argon-based aluminum HIPing treatments, while practically maintaining the as-recieved microstructure. These results show that better mechanical properties can be expected when using the suggested treatment without affecting the material fatigue resistance due to grain growth. The proof of concept presented in this work can pave the way to applying the new HHIPing approach to other AM metal parts.