Method for manufacturing a turbine wheel, hot isostatically pressed cast turbine wheel and turbocharger with such a

Abstract

A method for manufacturing a turbine wheel, comprising casting the turbine wheel from an austenitic nickel-chromium-based superalloy, subjecting the cast turbine wheel to hot isostatic pressing, and then subjecting a surface of the hot isostatically pressed turbine wheel to plastic deformation, wherein the hot isostatic pressing is carried out for a duration of 225 to 300 minutes at a pressure of 98 to 200 MPa and a temperature of 1160 to 1220°C. Furthermore, a hot isostatically pressed cast turbine wheel made of an austenitic nickel-chromium-based superalloy, wherein the turbine wheel has a plastically deformed surface, and a turbocharger containing such a turbine wheel are described.

Description

[0001] The present invention relates to a method for manufacturing a turbine wheel, in particular, but not exclusively, a turbine wheel suitable for use in a variable geometry turbocharger, a hot isostatically pressed cast turbine wheel and a turbocharger comprising a hot isostatically pressed cast turbine wheel.

[0002] Turbochargers are well-known devices for supplying air to the intake of an internal combustion engine at pressures above atmospheric pressure (boost pressures). A conventional turbocharger essentially comprises a housing containing an exhaust-driven turbine wheel mounted on a rotatable shaft connected downstream of an engine exhaust manifold. Rotation of the turbine wheel drives a compressor wheel mounted at the other end of the shaft. The compressor wheel supplies compressed air to the engine intake manifold. Turbines can be of the fixed-geometry or variable-geometry type. Variable-geometry turbines differ from fixed-geometry turbines in that the size of the turbine inlet channel can be varied to optimize gas flow velocities over a range of mass flow rates, thus allowing the turbine's power output to be varied to meet varying engine demands.

[0003] Due to the operating conditions to which conventional turbine wheels are subjected in service, they can fail as a result of fatigue. It would therefore be desirable to improve the fatigue strength or durability of turbine wheels. CN 103 433 435 A discloses a manufacturing process for a titanium alloy impeller. DE 34 46 176 A1 discloses a method for the heat treatment of superalloys prior to hot isostatic pressing. GB 2 499 669 A discloses a method for machining a metal / alloy article to seal open cavities.

[0004] One object of the present invention is to manufacture a turbine wheel that has improved fatigue strength or durability.

[0005] According to a first aspect of the present invention, a method for manufacturing a turbine wheel is provided, comprising casting the turbine wheel from an austenitic nickel-chromium-based superalloy, subjecting the cast turbine wheel to hot isostatic pressing, and then subjecting a surface of the hot isostatically pressed turbine wheel to plastic deformation, wherein the hot isostatic pressing is carried out for a period of 225 to 300 minutes at a pressure of 98 to 200 MPa and a temperature of 1160 to 1220°C.

[0006] By manufacturing the turbine wheel in this way, the present invention addresses problems associated with turbine wheel fatigue life and provides a turbine wheel that exhibits improved fatigue strength and durability compared to turbine wheels made from the same type of superalloy but which have not been subjected to hot isostatic pressing (HIP) followed by plastic deformation of a turbine wheel surface. The results of comparative tests, presented below, show that it is the combination of HIP and plastic deformation that ensures the improvement in fatigue behavior; performing either process alone does not guarantee the same degree of performance improvement.

[0007] Hot isostatic pressing can be performed at a pressure of 98 to 150 MPa, 98 to 125 MPa or 98 to 108 MPa.

[0008] Hot isostatic pressing can be carried out at a temperature of 1170 to 1215°C, 1180 to 1215°C or 1190 to 1210°C.

[0009] Hot isostatic pressing can be performed for a duration of 225 to 280 minutes, 225 to 265 minutes or 225 to 255 minutes.

[0010] In a preferred embodiment, hot isostatic pressing is carried out for a period of 225 to 280 minutes at a pressure of 98 to 150 MPa and a temperature of 1170 to 1215°C.

[0011] In another preferred embodiment, hot isostatic pressing is carried out for a period of 225 to 265 minutes at a pressure of 98 to 125 MPa and a temperature of 1180 to 1215°C.

[0012] In yet another preferred embodiment, the hot isostatic pressing is carried out for a period of 225 to 255 minutes at a pressure of 98 to 108 MPa and a temperature of 1190 to 1210°C.

[0013] The turbine wheel can be cooled after hot isostatic pressing and before plastic deformation. The turbine wheel can be cooled to any desired temperature to permit subsequent process steps, in particular to a temperature at which, but not limited to, the surface of the turbine wheel can undergo plastic deformation. For example, the turbine wheel can be cooled to approximately room temperature after isostatic pressing so that the subsequent plastic deformation process can be carried out accurately and effectively. The turbine wheel is preferably cooled to a temperature of approximately 18 to 25°C after hot isostatic pressing and before plastic deformation. The turbine wheel can be deformed at a rate of less than or equal to approximately...be cooled at 100°C per minute, or after hot isostatic pressing and before plastic deformation at a rate of less than or equal to approximately 50°C per minute, or after hot isostatic pressing and before plastic deformation at a rate of less than or equal to approximately 10°C per minute.

[0014] Plastic deformation can be achieved using any suitable process, such as laser peening, sandblasting, shot peening, etc., although shot peening is preferred. Shot peening can employ high-carbon cast steel in accordance with SAE J 827. Instead of, or in addition to, steel shot, wire shot, ceramic particles, and / or glass beads can be used. The jet can have a minimum size of S070 to S240 in accordance with SAE J 444. Preferably, the jet has a minimum size of S110 in accordance with SAE J 444, its physical and chemical properties being set forth below in the description of a particular embodiment. Shot peening can be performed at an intensity to achieve an Almen 'A' test strip arc height of 0.127 to 0.305 mm, 0.127 to 0.255 mm, or 0.127 to 0.203 mm, as measured in accordance with SAE J 442.

[0015] According to a second aspect of the present invention, a hot isostatically pressed cast turbine wheel is provided, which is made from an austenitic nickel-chromium-based superalloy, wherein the turbine wheel has a plastically deformed surface.

[0016] The turbine wheel according to the second aspect of the present invention can advantageously be manufactured using a method according to the first aspect of the present invention.

[0017] A third aspect of the present invention provides a turbocharger comprising: a housing; a turbine wheel supported on a shaft in the housing for rotation about a turbine axis; and a compressor wheel supported on the shaft in the housing, wherein the turbine wheel is a hot isostatically pressed cast turbine wheel made of an austenitic nickel-chromium-based superalloy, wherein the turbine wheel has a plastically deformed surface.

[0018] The turbine wheel used in the turbocharger according to the third aspect of the present invention can advantageously be manufactured using a method according to the first aspect of the present invention.

[0019] The production of a turbine wheel by a process according to the present invention, which comprises hot isostatic pressing followed by plastic deformation of a surface of the turbine wheel, results in a turbine wheel in which the plastically deformed surface exhibits various surface properties, such as surface texture, surface roughness, and / or color, compared to a turbine wheel produced from the same or a similar superalloy but not subjected to hot isostatic pressing followed by plastic deformation according to the present invention. It is understood that this provides a convenient means for characterizing and thereby identifying a turbine wheel produced according to the present invention.

[0020] A plastically deformed turbine wheel surface can exhibit a compressive residual stress of -1000 to -1500 MPa or -1100 to -1500 MPa at a depth of 25 to 90 micrometers below the surface of the turbine wheel, or a compressive residual stress of -1100 to -1500 MPa or -1200 to -1400 MPa at a depth of 30 to 60 micrometers below the surface of the turbine wheel. A plastically deformed turbine wheel surface can exhibit a compressive residual stress of approximately -1300 MPa at a depth of approximately 48 micrometers below the surface of the turbine wheel and / or a compressive residual stress of approximately -1150 MPa at a depth of approximately 80 micrometers below the surface of the turbine wheel.

[0021] A plastically deformed turbine wheel surface can exhibit a compressive residual stress of -500 to -1200 MPa or -500 to -1000 MPa at a depth of 100 to 190 micrometers below the surface of the turbine wheel (page 4), or a compressive residual stress of -600 to -900 MPa at a depth of 112 to 160 micrometers below the surface of the turbine wheel. A plastically deformed turbine wheel surface can exhibit a compressive residual stress of approximately -950 MPa at a depth of approximately 112 micrometers below the surface of the turbine wheel and / or a compressive residual stress of approximately -600 MPa at a depth of approximately 160 micrometers below the surface of the turbine wheel.

[0022] The turbine wheels and turbochargers of the aspects of the present invention defined above are particularly suitable for use with any type of internal combustion engine with a turbocharger, such as a diesel, gasoline direct injection or conventional spark ignition engine, where a more durable turbine wheel is desired or required.

[0023] High-pressure injection (HIP) is a form of heat treatment of a component under high pressure, which is applied to the component through a protective gas. It produces a component consisting of a completely dense composite material. The time spent at elevated temperature and pressure allows plastic deformation, creep, and diffusion to occur within the component material, thereby eliminating internal voids (i.e., porosity) that are naturally present in cast components.

[0024] Shot peening is a cold machining process in which a jet bombards the surface of a component to create a depression. To create the depression, the surface must yield under tensile stress, resulting in compressive stresses beneath the surface.

[0025] Without committing to any specific theory, it is assumed that the HIP process reduces the possibility of fatigue formation in the turbine wheel by eliminating internal porosity while simultaneously removing inconsistent residual stresses resulting from the casting process used to manufacture the turbine wheel. Subsequent plastic deformation of a turbine wheel surface induces compressive residual stress in the treated surface, reducing or preventing the formation and / or propagation of cracks throughout the wheel structure. Eliminating the casting residual stresses allows for an improved level of compressive residual stress through subsequent plastic deformation of the surface, for example, a shot peening process, ultimately leading to improved fatigue strength.

[0026] The turbine wheel can be made from any suitable austenitic nickel-chromium-based superalloy, for example one of the Inconel family of superalloys, such as Inconel 713C.

[0027] Although the manufacturing process of the present invention has been previously described in relation to the manufacture of turbine wheels, it is intended that the methodology of combining HIP with plastic surface deformation, for example shot peening, may be advantageous in the manufacture of other types of components using additive manufacturing techniques where porosity may have adverse effects.Another aspect of the present invention relates to a method for manufacturing a component, comprising casting the component, subjecting the cast component to hot isostatic pressing, and then subjecting a surface of the hot isostatically pressed component to plastic deformation, wherein the hot isostatic pressing is carried out with such pressure and temperature for a sufficient duration that internal porosity in the cast component is reduced or eliminated, and the component is given improved durability compared to the cast component before being subjected to the combined HIP and plastic surface deformation process.

[0028] Other advantageous and preferred features of the invention will become apparent from the following description.

[0029] Certain embodiments of the present invention will now be described purely by way of example with reference to the accompanying drawing; therein they show: Fig. 1 an axial cross-section through a variable geometry turbocharger comprising a turbine wheel according to a first aspect of the present invention; Fig. 2 a flowchart illustrating the steps involved in the manufacture of a turbine wheel by a method according to an embodiment of the present invention; and Fig. Page 5 3 shows a diagram of compressive residual stress versus depth below a surface of the turbine wheels which was treated (a) with HIP alone, (b) with HIP and shot peening combined according to the present invention, (c) with shot peening alone and (d) with shot and sandblasting.

[0030] Fig.Figure 1 represents a variable geometry turbocharger comprising a housing containing a variable geometry turbine housing 1 and a compressor housing 2, which are connected by a central bearing housing 3. A turbocharger shaft 4 extends from the turbine housing 1 through the bearing housing 3 to the compressor housing 2. A turbine wheel 5 is mounted at one end of the shaft 4 for rotation with the turbine housing 1, and a compressor wheel 6 is mounted at the other end of the shaft 4 for rotation with the compressor housing 2. The shaft 4 rotates about the turbocharger axis 4a on bearing assemblies positioned in the bearing housing 3.

[0031] The turbine housing 1 defines an inlet spiral 7, into which gas from an internal combustion engine (not shown) is supplied. The exhaust gas flows from the inlet spiral 7 via an annular inlet channel 9 and the turbine wheel 5 to an axial outlet channel 8. The inlet channel 9 is defined on one side by a surface 10 of a radial wall of a movable annular wall element 11, commonly referred to as a "nozzle ring," and on the opposite side by an annular cover band 12, which forms the wall of the inlet channel 9 facing the nozzle ring 11. The cover band 12 covers the opening of an annular recess 13 in the turbine housing 1.

[0032] The nozzle ring 11 supports an arrangement of inlet blades 14 spaced evenly around the circumference, each extending over the inlet channel 9. The blades 14 are oriented to deflect gas flowing through the inlet channel 9 in the direction of rotation of the turbine wheel 5. When the nozzle ring 11 is near the annular cover band 12, the blades 14 project through suitably configured slots in the cover band 12 into the recess 13.

[0033] The position of the nozzle ring 11 is controlled by an actuator arrangement of the type disclosed in US 5,868,552. An actuator (not shown) can be operated to adjust the position of the nozzle ring 11 via an actuator output shaft (not shown) connected to a yoke 15. The yoke 15, in turn, engages axially extending actuating rods 16 that support the nozzle ring 11. Accordingly, by suitable control of the actuator (which may be, for example, pneumatic or electric), the axial position of the rods 16, and thus of the nozzle ring 11, can be controlled. The rotational speed of the turbine wheel 5 depends on the velocity of the gas flowing through the annular inlet channel 9. With a fixed mass flow rate of the gas flowing into the inlet channel 9, the gas velocity is a function of the width of the inlet channel 9, the width being adjustable by controlling the axial position of the nozzle ring 11. Fig.Figure 1 shows the fully opened annular inlet channel 9. The inlet channel 9 can be closed to a minimum by moving the surface 10 of the nozzle ring 11 towards the cover band 12.

[0034] The nozzle ring 11 has axially extending radially inner and outer annular flanges 17 and 18, which extend into an annular cavity 19 provided in the turbine housing 1. An inner and outer sealing ring 20 and 21 are provided to seal the nozzle ring 11 with respect to the inner and outer annular surfaces of the annular cavity 19, respectively, while allowing the nozzle ring 11 to slide within the annular cavity 19. The inner sealing ring 20 is supported in an annular groove formed in the radially inner annular surface of the cavity 19 and bears against the inner annular flange 17 of the nozzle ring 11. The outer sealing ring 21 is supported in an annular groove formed in the radially outer annular surface of the cavity 19 and bears against the outer annular flange 18 of the nozzle ring 11.

[0035] Gas flowing from the inlet spiral 7 to the outlet channel 8 flows over the turbine wheel 5, and consequently torque is applied to the shaft 4 to drive the compressor wheel 6. As the compressor wheel 6 rotates in the compressor housing 2, ambient air present in an air inlet 22 is pressurized and the compressed air is delivered to an air outlet spiral 23, from where it is supplied to an internal combustion engine (not shown).

[0036] The in Fig. The turbine wheel 5 shown was designed as described below with reference to Fig.The manufacturing process is explained in section 2. In step 201, the turbine wheel is cast from a suitable austenitic nickel-chromium-based superalloy, such as Inconel 713C, using a conventional precision casting process. In step 202, the cast turbine wheel is subjected to hot isostatic pressing for 240 ± 15 minutes at a pressure of 103 ± 5 MPa and a temperature of 1200 ± 10°C. In step 203, the turbine wheel is cooled to 18–25°C at a rate of less than 10°C per minute. Page 6 In step 204, a surface of the turbine wheel is shot-blasted using a jet of high carbon cast iron according to SAEJ827 with a minimum size of S110 according to SAEJ444 and an intensity to achieve an Almen 'A' test strip arc height of 0.127 to 0.203 mm, measured according to SAEJ442.In step 204, it is preferred that as far as possible 100% of the outer surface of the turbine wheel is subjected to shot peening, with the exception of the rear weld stud area of ​​the turbine wheel, which ideally is not shot peened, for example by some form of suitable covering applied to this region of the turbine wheel prior to shot peening.

[0037] SAE J 827 is the international standard that specifies the requirements for chemical composition, hardness, microstructure, and physical properties for blasting high-carbon steel for use in shot peening applications. The blasting characteristics according to SAE J 827 and with a minimum size of S110 according to SAE J 444 are outlined below. Chemical composition: element % carbon 0,8-1,2 manganese 0,6-1,2 silicon minimum 0.4 sulfur maximum. 0.05 phosphorus maximum. 0.05 Microstructure: Uniform tempered martensite Hardness: SAEJ827 specification. 40 to 51 HRC. Bulk density: mind. 7 g / cm 3 Deficiencies: to comply with ISO 11124 / 3 and SAEJ827 tolerance sieve number mm Everything passed through 30 sieves 0,600 Minimum 10% retained 35 sieves 0,500 Minimum 80% retained 50 sieves 0,300 Minimum 90% retained 80 sieves 0,180 Nominal size: 0.30 mm

[0038] The residual stress at various depths below the surface of the turbine wheels, which were subjected to (a) HIP alone, (b) HIP and shot peening combined according to the present invention, (c) shot peening alone, and (d) shot and sandblasting, is determined in Fig. Figure 3 shows that the turbine wheel produced according to the present invention exhibited residual stress over a large depth range of 16 to 224 micrometers (µm), the magnitude of which was greater than that of the three turbine wheels produced using alternative methods comprising only HIP or plastic deformation alone.

[0039] A comparative test of turbine wheels manufactured using different methods was conducted to investigate the approximate fatigue life under high cycle load (HCF life). The results are presented below. The results for the turbine wheel manufactured according to the method of the present invention are underlined and clearly demonstrate an improvement in durability. Manufacturing process - Minimum lifespan (hours) - Maximum lifespan (hours) - Average lifespan (hours) Number of data points No HIP or bullet-staffing 1,6 18 10 30 Only HIP 2 9 5,5 10 Only shot peening < 1 12 6,5 10 HIP & Shot Blasting 4 40 22 20

Claims

[1] Method for manufacturing a turbine wheel, comprising casting (201) the turbine wheel (5) from an austenitic nickel-chromium-based superalloy, subjecting the cast turbine wheel to hot isostatic pressing (202) and then subjecting a surface of the hot isostatically pressed turbine wheel to plastic deformation (204), wherein the hot isostatic pressing is carried out for a period of 225 to 300 minutes at a pressure of 98 to 200 MPa and a temperature of 1160 to 1220°C. [2] Method according to claim 1, wherein the hot isostatic pressing (202) is carried out at a pressure of 98 to 108 MPa. [3] Method according to claim 1 or 2, wherein the hot isostatic pressing (202) is carried out at a temperature of 1190 to 1210°C. [4] Method according to claim 1, 2 or 3, wherein the hot isostatic pressing (202) is carried out for a period of 225 to 255 minutes. [5] Method according to a preceding claim, wherein the turbine wheel (5) is cooled to a temperature of approximately 18 to 25°C (203) after hot isostatic pressing (202) and before plastic deformation. [6] Method according to claim 5, wherein the turbine wheel is cooled after hot isostatic pressing (202) and before plastic deformation (204) at a rate of less than or equal to approximately 100°C per minute. [7] Method according to claim 5, wherein the turbine wheel is cooled after hot isostatic pressing (202) and before plastic deformation (204) at a rate of less than or equal to approximately 10°C per minute. [8] Method according to a preceding claim, wherein the plastic deformation is achieved using shot peening. [9] Method according to claim 8, wherein the shot peening uses high carbon cast steel according to SAEJ827. [10] Method according to claim 8 or 9, wherein the beam has a minimum size of S070 to S240 according to SAEJ444. [11] Method according to claim 8 or 9, wherein the beam has a minimum size of S110 according to SAEJ444. [12] Method according to any one of claims 8 to 11, wherein the shot peening is carried out with an intensity to achieve an Almen ‘A’ test strip arc height of 0.127 to 0.305 mm, as measured according to SAEJ442. [13] Method according to any one of claims 8 to 11, wherein the shot peening is carried out with an intensity to achieve an Almen ‘A’ test strip arc height of 0.127 to 0.203 mm, as measured according to SAEJ442. [14] Hot isostatically pressed cast turbine wheel (5) made of an austenitic nickel-chromium-based superalloy wherein the superalloy has no internal cavities and wherein the turbine wheel has a plastically deformed surface exhibiting a compressive residual stress of -500 to -1200 MPa at a depth of 100 to 190 micrometers below the surface of the turbine wheel. [15] Turbocharger comprising: a housing (1); a turbine wheel (5) supported on a shaft (4) in the housing for rotation about a turbine axis; and a compressor wheel (6) supported on the shaft (4) in the housing (1), wherein the turbine wheel (5) is a turbine wheel according to claim 14.

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