GB2265155A

GB2265155A - Metal powder consolidation

Info

Publication number: GB2265155A
Application number: GB9305068A
Authority: GB
Inventors: Andrew Richard Jones
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1992-03-18
Filing date: 1993-03-12
Publication date: 1993-09-22
Also published as: GB9206119D0; GB9305068D0

Abstract

A method of consolidating a body of a mechanically-alloyed powder material, comprising the operations of heating a pre-cursor mechanically alloyed powder material in such a manner as to cause transient melting of the precursor material and quench casting the molten precursor material onto a pre-form.

Description

Metal Powder Consolidation This invention relates to the consolidation of metal powder, and more particularly to the consolidations of mechanically-alloyed (hereinafter referred to as "MA") metal powder. MA powders are well known in the art and are usually consolidated by high temperature solid state processes. Typically these will involve placing the powders in a mild steel container which is then degassed, sealed and hot consolidated by either hot isostatic pressing (hereinafter referred to as "HIP") forging, or extrusion process.

Current knowledge of the release condition and subsequent performance of Fe-based oxide dispersion strengthened (hereinafter referred to a "ODS") MA materials suggests that defects and other inhomogeneities from the MA processing are either entrained in the finished producs as intrusions, or produce undesirable end microstructures. Features which have been identified and are known to be deleterious include: (i) Intrusions Intrusions are fragments of the original MA powders (typically, 5-20pm). They tend to be surrounded by particulate debris, and do not sinter into the finished product. It has been demonstrated that such defects influence grain structures in the finished product and creep fracture paths interlink through these defects when present.

(ii) Inhomoqeneous Alloying This can occur locally on a scale from some micrometers down to some tens of nanometers.

According to the present invention there is provided a method of consolidating a body of a mechanically-alloyed powder material, comprising the operations of heating a pre-cursor mechanically alloyed powder material in such a manner as to cause transient melting of the precursor material and quench casting the molten precursor material onto a pre-form.

Advantageously, the metal powder may be quench cast onto a shaped preform by a plasma-spray deposition process. The preform with the plasma-spray deposited metal powder thereon subsequently may be processed by conventional means.

The MA metal powder consolidated in accordance with the invention should contain fewer of the aforementioned defects and inhomogeneities, and the transient melting of the invention should cause little loss or coarsening of dispersoids.

The invention therefore includes a mechanicallyalloyed metal powder consolidated in accordance with the invention.

Production of a preform requiring further processing should allow the appropriate level of work to be introduced in a form suitable to engender, by intermediate and final heat treatments, any anisotropic or gross grain structures which may be desirable in the product in the release condition.

Although the invention has been described in relation to Fe-based alloys it will be understood that it may be used with some other MA metal powders.

It will also be appreciated that other processes may be used as an alternative to plasma-spray deposition techniques to produce the transient melting of the invention.

EXAMPLE A Fe-based MA powder of about 100cm mean particle size is sieved to avoid substantially larger particles.

A mandrel of 150 mm diameter and 1 metre length is rotated. The sieved MA powder is plasma-sprayed in either an Ar/H2 or an Ar/He gas mixture on to the mandrel at a deposition rate between 25 and 30g/min to produce a tubular preform growing by about 6mm thickness in a 7 hour period.

Subsequent to the plasma-spraying the tubular preform is treated conventionally, e.g. extrusion, tube sinking, heat treatment, etc.

Examples of suitable MA powders are: (1) ODM 751 (Dour Metal SA-Belgium).

MA956 (Inco Alloys International) PM2000 (PM Hochtemperatur-Metall GmbH) It will be understood that other suitable MA powders and alternative mandrels or formers may be used.

Claims

1. A method of consolidating a body of a mechanicallyalloyed powder material, comprising the operations of heating a pre-cursor mechanically alloyed powder material in such a manner as to cause transient melting of the precursor material and quench casting the molten precursor material onto a pre-form.

2. A method according to Claim 1 wherein the metal powder is deposited on the preform by a plasma-spray deposition process.

3. A method according to Claim 2 wherein the pre-form together with the deposited material is subjected to a processing operation.

4. A method according to any of Claims 1 to 3 wherein the mechanically-alloyed powder material is an iron-based alloy.

5. A mechanically-alloyed metal powder artefact wherein the mechanically-alloyed powder has been consolidated by a method according to any of Claims 1 to 4.

6. A method of consolidating a body of mechanicallyalloyed powder material substantially as hereinbefore described.