GB2164664A - Production of alloys by deposition from vapour and apparatus therefor - Google Patents

Abstract

An alloy 40 produced by deposition of the constituents from the vapour phase onto a temperature controlled collector 10 within a vacuum chamber is peened by relatively hard rounded balls 38 directed at the surface during the deposition process. The purpose of the peening operation is to level the surface and to cause renucleation thereby minimising porosity due to shadowing by the growing metal crystals. A secondary purpose is to control the residual stresses in the deposit. The balls 38 are propelled at the deposited alloy by impeller 22 and brushes 33, 34 prevent loss of balls which are returned to peening device 12 via conduits. <IMAGE>

Description

SPECIFICATION Improvements in or relating to the production of alloys and apparatus therefor The present invention relates to the mechanical working of metals and in particular to metals produced by deposition from the vapour phase.

Processes for the production of bulk alloys by deposition of the constituents from the vapour phase are known. Examples of such processes and apparatus therefor are described in UK Patents 1 206 586,1 1 265965 and 2079324. One of the problems of such processes, however, is that they need to employ a high vapor flux so that the required thickness of alloy is deposited within a practicable time. A result of this is that preferential growth of some crystallographic planes produce asperities on the deposit which tend to cause 'shadowing' on the moving collector resulting in porosity being generated in the deposit. It is necessary therefore, in order to prevent in the deposit. It is necessary, therefore, in order to prevent or minimise such porosity to condition the surface of the alloy during the deposition process.UK Patent 1 521 293 describes a method and apparatus for mechanically working the deposited alloy by peening with a rotatable flail device.

The device causes renucleation of the growing metal crystals to control preferential crystal facet growth.

Flailing flattens the asperities that form but coverage tends to be insufficient and in order to improve coverage the flailing speed must be increased. Increased speed results in a deep worked layer which is metallurgically undesirable; the structure is unstable and residual stresses are high. Other problems include wear of the device itself.

UK Patent 1 605035 describes a process for producing metal articles by spray depositing metal onto a substrate whilst simultaneously bombarding the deposit with hard rounded particles. The use of ball-peening in the above process provides a method of hot working the deposit during spray deposition.

Stated benefits of hot working the sprayed deposit are recrystallation, fine grain size, high density and a lack of residual tensile stresses which would otherwise lead to cracking of the deposit.

The use of ball-peening an alloy produced by condensation from the vapour phase allows random coverage of the surface being worked and also greater control of the degree of working applied to the surface and, therefore, control of residual stresses.

Therefore, according to one aspect of the present invention a process for the production of bulk alloy by deposition of the alloy constituents from the vapor phase onto a temperature controllable collecting surface within a vacuum chamber includes the improvement wherein the surface of the alloy deposit is subjected to deformation by peening by relatively hard rounded balls directed at the surface of the alloy deposit during the deposition process.

In the context of th is specification as applied to the present invention the term 'deformation' is intended to mean, unless otherwise state, only sufficient mechanical working as may be required to cause flattening of the deposit, renucleation of the growing metal grains and control of residual stresses and not gross plastic mechanical working of the alloy deposit. In the process and apparatus described in UK Patent 1 605 035 both the stream of sprayed metal and the stream of peening balls are directed downwards onto the target area and the balls are then retrieved from the bottom of the apparatus and recycled upwards to the ball slinger.In the present invention because the metal stream is a vapour flux travelling substantially vertically upwards from one or more molten metal sources it is not possibleto allow the peening balls unrestricted rebound travel after striking the deposit surface. The balls must of necessity be prevented from falling into the molten metal source.

According to a second aspect of the present invention apparatus for the production of bulk alloy by deposition of the alloy constituents from the vapour phase onto a temperature controllable collecting surface within a vacuum chamber includes a vapour source, peening means comprising a supply of relatively hard rounded balls, means to propel the balls at an alloy deposit on the collecting surface and means to contain balls rebounding from the alloy deposit surface from entering the vapour source.

In one embodiment of the present invention the temperature controllable collecting surface may be of cylindrical form and the peening means comprises a mechanically driven paddle bladed impeller having a plurality of blades to propel the balls at the alloy deposit, the impeller being rotatable within an enclosure having an opening onto the alloy deposit and the enclosure being sealed to the collector surface by rubbing brushes to prevent significant loss of peening balls.

The peening balls may be made of any suitable material which is resistant to fracture under the conditions of operation. In practice the peening balls may be chosen for their density which may produce the desired degree of working of the deposit when propelled at a suitable velocity at the deposit. Materials ranging from fused quartz at the low density end of the scale to tungsten at the other end may be employed.

Because of the inherent limitations of other mechanical working systems which have been used in the past it has been necessary, in order to obtain sufficient area coverage of deformation achieved, to move the collector relatively slowly. This has lead to relatively thick incremental layers of alloy being deposited. It is desirable in the interests of lower levels of contamination per layer to run the collector at higher rotational speeds and produce layers of lower incremental thickness. Because of the greatercontrolability of the ball peening technique it is now possible to utilise much lower incremental thicknesses whilst still achieving adequate area coverage of the deposit.

In order that the invention may be more fully understood one embodiment will now be described by way of example only with reference to the accompanying drawings, of which: Figure 1 shows a general arrangement of a peening device in relation to part of a cylindrical collector and an evaporating source.

Figure 2 shows a sectional side elevation of the construction of a peening device according to the invention.

Figure 3 shows a view of a fixture for the peening-ball retaining brushes.

Figure 4 shows a top view of a section of the peening device.

Refering now to Figure 1, this shows a cylindrical collector of diameter 400 mm and 60 mm width generally at 10. Below the collector is an evaporator source 11. Sited in the lower left hand quadrant is the peening device shown generally at 12. The above items are contained within a vacuum chamber 13 (not shown).

Reference will now also be made to Figures 2,3 and 4 and the above items will be described in greater detail, the same items in the various figures having common reference numerals. The peening device 12 comprises a generally 'C' shaped member 20 and side plates 21 forming a housing. Within the housing is an impeller shown generally at 22. The impeller 22 comprises a cylindrical portion 24 having integral vanes 25, a shaft 26 running in ball-bearings 27. Neoprene rubber vane extensions 28 are located in slots 29 in the vanes 25 by rivets 30. The housing formed by the members 20 and 21 also includes a mouth portion, shown generally at 31 opening onto the collector 10. At the mouth portion 31 is a fixture 32 which carries two rows of metal wire brushes 33 and 34 which form a rubbing seal between the peening device 12 and the collector 10.Formed between the fixture 32 and the side plates 21 and in the side plates 21 are conduits 35 leading from between the brush rows 33 and 34 to the interior of the housing formed by members 20 and 21. Drive means 36 (not shown) are provided to rotate the impeller 22 by the shaft 26. In the interior of the housing formed by the members 20 and 21 is a ramp 37 and a supply of steel balls of 1.2 mm diameter 38 (the balls being shown collectively as dashed lines indicating flight paths). On the collector 10 is an alloy deposit 40.

In operation the collector 10 rotates in a clockwise direction at a speed generally in the range 1 to 20 rev/min. Alloy vapour from the evaporator 11 condenses on the surface of the collector 10 to form the alloy deposit 40. At each revolution of the collector 10 a thin layer, generally around 5 M > m, of alloy is deposited.

The impeller 22 is rotated in an anticlockwise direction at 1750 rev/min by the drive means 36 (not shown).

The steel balls 38 are propelled at the deposit 40 and after striking it rebound into the upper region of the housing formed by the members 20 and 21. The ramp 37 dictates a minimum trajectory angleforthe balls 38. This prevents balls from being incident normally on the deposit 40 and rebounding into the path of oncoming balls thus minimising unproductive collisions between the peening balls 38. As the collector 10 rotates the brushes 33 and 34 rub on the surface of the deposit 40 forming a seal and preventing the loss of peening balls 38 from the peening device 12. Some balls inevitably pass through the first brush row 33 and in so doing become trapped in the channel between brush 33 and brush 34. Balls thus trapped return to the housing interior via the conduits 35 aided by gravity and the inherent vibration of the device.The purpose of the rubber vane extensions 28 is to prevent seizure of the impeller 22 by balls becoming jammed between the solid vanes 25 and the 'C' shaped housing member 20. Peening balls 38 rebounding from the deposit 40 strike the upper section of the member 20 and are mostly deflected downwards towards the impeller 22 and become entrapped in the spaces between the vanes and extensions 25 and 28 and the member 20 thus being recycled and propelled again at the deposit 40.

Table 1 shows the variation in surface coverage with the number of peening balls and the speed of rotation of the impeller per revolution of the collector.

TABLE 1 No. of balls Speed of impeller (rev/min) 1250 1500 1750 3000 3% 5% 6% 6000 6% 8% 9% 9000 8% 10% 13% 12000 8% 10% 12% Examination of the peened surface has shown that the peening effect is random in its surface coverage unlike earlier peening methods. The figures shown in Table 1 are those achieved on the equipment described above where the impeller diameter is approximately 87 mm.

It is envisaged that on commercial scale apparatus the collector size will be of much larger dimensions, perhaps of the order of 3 m in diameter, and that peening devices also of larger dimensions will be employed increasing the efficiency of area coverage of the device.

Where the collector is also of much greater width than described above it may be advantageous for the housing and impeller to be divided up into discrete compartments by thin partitions. The purpose of this is to prevent any migration of the peening balls towards one end of the peening device. Where a large collector is employed an alternative to scaling up the peening device in rough proportion to the collector size would be to employ two or more banks of devices situated in the lower left or lower right hand quadrants or both.

Alternative brush materials are also envisaged. In the embodiment described above metal wire brushes are described to effect peening ball containment. Brushes made of polymer fibres or other non metallic materials such as glass may also be employed.

The impeller vane extensions described above are in neoprene rubber, however, any suitable material of a resilient nature may be employed to prevent jamming of the impeller. Extensions comprising thin spring steel tips may be employed to minimise the wear of the rubber extensions.

Alternative peening ball recycling may also be employed where after striking the deposit collector they are gathered in a lower gallery and redistributed by mechanical means to the impeller(s). An essential requirement, however, is that any ball peening system must be capable of excluding the peening medium from the evaporator source. An additional safety feature against possible contamination would be to screen the vapour source to prevent any stray peening balls from entering.

Further alternative constructions of ball throwers are also envisaged including those which employ a ball feed co-axial with the impeller. Such a system may obviate the need for flexible, resilient vane extensions and thus simplify the apparatus.

Where the alloy being produced would tolerate an atmosphere such as helium, argon or hydrogen for example, an alternative means of propelling the peening balls may be by gas pressure from one or more barrels. Peening balls may then be collected in a lower gallery and redistributed to the propelling means by means dependent on gas pressure.

Means are also envisaged whereby the position of the peening device(s) may be adjusted with respect to the collector as the thickness of the alloy deposit increases.

Although one embodiment and various alternatives are described above by way of illustration only, the essence of the invention will be clear to those skilled in art and further mechanical alternatives and variations will become apparent without departing from the scope dfthe present invention.

Claims (5)

CLAIMS 1. A process for the production of bulk alloy by deposition of the alloy constituents from the vapour phase onto a temperature controllable collecting surface within a vacuum chamber includes the improvement wherein the surface of the alloy deposit is subjected to deformation by peening by relatively hard rounded balls directed at the surface of the alloy deposit during the deposition process. 2. Apparatus for the production of bulk alloy by deposition of the alloy constiuents from the vapour phase onto a temperature controllable collecting surface within a vacuum chamber includes a vapour source, peening means comprising a supply of relatively hard rounded balls, means to propel the balls at an alloy deposit on the collecting surface and means to contain balls rebounding from the alloy deposit surface from entering the vapour source. 3. Apparatus according to claim 2 and wherein the means for propelling the balls at the alloy deposit surface comprises a mechanically driven paddle bladed impeller having a plurality of blades, the impeller being rotatable within an enclosure having an opening onto the alloy deposit and the enclosure being sealed to the collecting surface by brushes to prevent significant loss of peening balls. Amendments to the claims have been filed, and have the following effect: *(b) New or textually amended claims have been filed as follows:

1. An alloy deposition apparatus operable by deposition of alloy from the vapour phase, comprising a vacuum chamber, an evaporator and a rotatable drum collector both within the vacuum chamber, means operable to propel peening balls against alloy deposited upon the collector surface within the vacuum chamber and with staggered trajectories so as to effect peening of an area of alloy deposit at any instant, means operative to prevent perpendicular incidence of the peening balls upon the collector to minimise rebound collisions, and a containment means operative to contain peening balls on rebound from the collector and keep them from reaching the evaporator.

2. An alloy deposition apparatus as claimed in claim 1 in which the means operable to propel the peening balls is a rotatably driven paddle bladed impellor.

3. An alloy deposition apparatus as claimed in claim 2 in which the containment means is a housing enclosing the impellor and having an opening onto the surface of the collector, and in which the impellor has flexible blade tips to prevent peening balls being trapped between the blades and the housing.

4. An alloy deposition apparatus as claimed in any one of the preceding claims in which the peening balls are constrained to a sector of the collector by rubbing seals operable there against.

5. An alloy deposition apparatus as claimed in claim 1 and substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.